In what ways is the word “work” as used in everyday language the dlemuxxc05z6hm1 wx/6+ jq6vsame as that defined in physics? In what ways is it different? Give examples oz+vm1x 566e 6x/ qdwxmlhj0ucf both.

Can a centripetal force ever do workrpqys a7tyj;umo) s bf3w 7fo-(0oa8kyb/9 3 e on an object? Explain.

Can the normal force on an object ever do work uj. eq*0w0bce (-mbw c1hkm4*bc(5 qor8jef g? Explain.

A woman swimming upstream is not movic 65i25rx i 1 i+pehi7npff-gqng with respect to the shore. Is she doing any work? If she stops1p5i g5-i chx ie2qpff 7nr6+i swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hing0sb-ca/c2* v f0owvht: Consider what happens to the dishes when you pull a tablecloth out from under thh-* f/wvcg so020b avcem.]

Why is it tiring to push hard against ao)5+j fgzl5 yuy7qql/7+azkg solid wall even though you are doing no woz uqgf5+/75o) lza +yq7kgj lyrk?

You have two springs that cj- zfu*jxwq dw/x8m :5wpdu i9h9/3kare identical except that spring l is stiffer than sprin5-m du*8zjwj9/iwq dh 93xk:pc / ufxwg 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is frew5nm wq isv6t9d6w4 b5e to slide on a frictionless surface (Fig.6-30). The block starts from 9b6 w5n mq46sw dti5wvrest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential en *qia,;vospnp+ o+td 9ergy change when you jump as high as y*ad i ;n+ tspv9+pooq,ou can?

In Fig. 6–31, water ballo25zo1e-gra ln-m y82f,c5pi r lq :xblons are tossed from the roof of a building, all with the same speed but with-nlb8f-e gil:qr22 p 1alr5 cyo xm5z, different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point thalf,ve r+ pofogd*(:c )t is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the secono,ovfr egc:d(*lf + p)d launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright 2v:8rp qo/p wenoi,da(*bl3 b nok (x8on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explaina2nb (8xw :pqool*p b (,nvodk/38eir, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The insdmo;mf, 61wjd5b e / t+e85ae8bo nnurtructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructoru;jw btm em8 5+dd 81ea/nn,5e6br oof is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when watcmuy, o (5kwm3er at the top of a waterfall falls tw,o3m( m5ucyk o the pool below?

Describe the energy transformations when a child hopsjags 2g93v/m r around on a pogo stick.

Describe the energy transformations that take place when a ski:6mr4eb)bc) ptwt/o9/w ol oser starts skiing down a hill, but roopew)m 9bwl o6bt)s/4: t/cafter a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts ftkqz )f*b8 / 3te*uenvrom rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) ut* vfkb/n 3e8t*q) ezit is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen feix f*:gx7wu ck0l5+z kv)/o hm+ u4wlog in their path rather than stepping on top and jumping down on the ot:4lfux *f/owhkz7cu)5wmvi+0kg+ x eher side. Explain.

Two identical arrows, one with twice the speed of the othesm9u+ls1g m3;aaj z9 or, are fired into a bale of hay. Assuming the hazj u3am ms;g91l9 so+ay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms ofq usk*o.e+0v;,vak+akpz:fhqw* ;qc xk5cw 1 energy, (a) ignoring frict,1 kcq kuq05cz;k v+s*qf poah;*w: xv.ae+wk ion, and (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height go.i jpu2 lb8sis3-6yuo 9(+mymu ttb 7reater than its original heig6+(jblbs p8i m7ousu y3-9y2 uottm.iht? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do ozcpvdon e7s9nu43v+: xa ws51n the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the tadpo v 4cnu5ssa9 7+v3z1nxe:w ble, and (d) the weight of the suitcase?

Repeat Question 22 for thgx2wb-xf (;cve power needed rather than the work.

Why is it easier to climb a zxz, z5t5n3uoc+ fau7mountain via a zigzag trail than to climb straight up?5utz 5unx +,73 ozczaf

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to deppn cbq6nr6 tp -0e-2xcrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much ropenbc6xpe 260t-nq-pp r must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitationacdik ; ma ,n(-yr;m+tll force when a 265-kg pile driver fallsmyt(l card ;n,;km-+i 2.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20 w)bndcqh ,fc(v97/: w6c h d),wjzzl yz;i,wt.0 m high. How much work is required? c,7c,lw ,hnvd;:)hj cwy/zdqwft 9wz(6b i)z    J

  A 1300-N crate rests on the floor. How much work is required to move it 7l5f wugkz f s0iy ivz3ls0c2r6p1/,y at constant speed (a) 4.0 m along the floor against a friction forcsf zg3iy u 2lyif0l15zrw76 /pk,sc0v e of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the:zcq6,gpd*fq 9a3fmh movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if thga mh 6cq*dp ,qf9z3:fe effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of1mv zr 96yw/p 7fio.jfryw5 3d5h-2vw urcnw7 for 7.0 s. Find the net workyru57hvf2drw ncwf1/6yw oj .ri9z5wv-m7 3p done on the box.   J

  Eight books, each 4.3 3 ydv(z.7ruvaalp 1otk.j 3k j7bk1*qcm thick with mass 1.7 kg, lie flat on a table. How much w*p.drb1v y7v3ljka 3ojzatkq( 7k. u1 ork is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we mii kn2fcg5.rk b(i/ agqfio )0-ght not otherwise be ableqkf ria g0g.2) k/-n5(fioibc to liff. Show that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 mn1ixr (gya qi-7v5tl, down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incligtnvrqi-ix , 5 a(7yl1ne (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acmh*3ywt5tz1 s celeration of 0.10 g upwwyszm h5*tt31 ard.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is linear ane(*ase;mbbz (cq6yx .) *mbi fd that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies aq uk;7bf05q+,cewlaps shown in Fig. 6–37. Determine the work done by this for0k7 lb5ae+cq,fpu w;qce to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle :y /fm54qp wm x8ivb8uacts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen moleculewg*8w:p v /gle, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by whatv s()a(khh5/a p xb5stp tf eciwh(6-) factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requw,*b2mphqbu c +wfn39ired to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 129 es*ras6/:1 jppttwq7 z: dud ;j/riw50-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force of en2g -xi 3m40kk s) )uq5exhh6deirz2110 N on the arrow over a distance of 78 cm. What is )uei- esxgn)r k2hk md4i0ex5zqh623the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backw n fpk z1r7;*dlwkrm+2ard 25 cm when the ball is caught. What wap2 d1w m 7lfn*;+rrkkzs the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factortr*kdr.*e oppj003ak will its minimum braking distance be increased, assuming all else is the same? Ignore the drivedr r 3*jt0k.k0epop*ar’s reaction time.

  At an accident scene on a level road, ins8ci 0fcy0u6sbf2m+ k b r-h5xvestigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locss0 bkx628c 0f+myubfrch -5 iked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pnnpk7tqh;ub 4fg )23ditched at By the time it reaches the plate, it may hav bf)h;ku 23 qntn4gdp7e slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thr d2y8dk92foz;kz bqu)own straight up by someone who does 80.0 J of wor zk28z2dqo; ufd)y9 kbk on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acce9na r(8f-bq fr+qbw( qleration by a single cable. De-(rb(qb 89+ nffawqrq termine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constai n.52pc yyhe8e)gijt;s p95ant, k, of 440N/m How much must this spring be stretched to store 25 J of potential energy? tjagciinpyshy852 ;5) p.e e9   m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher.o6pz/k -kit :c*,rsscvv:;dy What is the change in poten:yk,- rd;i/p 6 vtscvok zs*c:tial energy?    J

  By how much does the gravi7 (vcu3jjti n(tational potential energy of a 64-kg pole vaulter change if his center of mass rises about c(vt7j u3jn (i4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v =y6r5 5 b wngsu2ko;eb; 65 km/h when it strikes a horizontal coiled spring and is brought to rs5weunb 2 ko;6g;ryb5est in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m above cdt+aczth*.pd . b7 mv6zy90rthe ground. What is the potential energy ob6 rd z.tv dm7t.0*9+p cachzyf the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs totyf6q i 7n(ko3m4i*zj the top of a 3300-m q f37(* ionji6km4 zytpeak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs v2/tnqtd5b5gb w k8sq6e +bvp. gl 6,jbertically next to a ruler. The end of the spring is l wb56tp6vdjets8 bbkq2nq,/g5g b.+ next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarza/dc f01+,yet 4ad htoan, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the ja1f+e0t/ht4,yd co a dungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a oeb we8-ci+p 7q54acf frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially give;m-wl qz tj:t,n a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic emu/1ndq k8o(x ilm5 q7nergy is transformed into gravitational potential energy without the aid of a pole. With what minimum speedqnlm5 md7/uq1k( 8 ixo must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps verticall3 2yma8 pbppw.y upward from the top of a platform with a spee2ywp mb38.ap pd of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignors(0; -t9 ,qqrl0 ij 6ojr,swwxwkvp 5me its mass), whose spring stiffness constant is 950N/m is atta( -,qw5ikp strxj ,w;mw96 00jvs roqlched to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the loope9, an l4z9vsexd track shown in Fig. 6–39. If the block is to remain on the traczex49a l9, nvsk, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached 7eu e8i qmlb+:to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initiali7 eqlu+ e:b8m displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a brido wq6f f*4kn2l10f adm/fsnh)ge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness cons6f*1naffqkf4so m0h /wd)n2ltant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to poi 2(xb+oimgm:q nt 1 where it is released from rest. Assuming no friction, calculate the speed at poinb(x+goim2 :q mts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/pshvo;m: 1 gt a8dj.c*s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at thek uzi-) c;dbr6b;p :nq bottom of an elevator shaft. If the elevator cable should break when the elevator rc dp:i;bbqnz;6) uk-is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle sxiy4r w(,(xr up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 ap hpvk6m*3 s,kg and traveling 95km/h in opposite directions, collide head-on a* 3a 6mvhkpps,nd come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the bottom with a speedgz9yv je-e 0+l of 2.2m/s How much thg eljvz+ye -09ermal energy due to friction was generated in this process?    J

  A ski starts from rest ae+cy lqd3h7wabxt8h 12 z90 upewk* q9nd slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tragl63x:+dt z/sw 3cblfbc7mn2 ,.lk fee 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1.5 0u24tlyi eez8 m8il42uee0 t zy.
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, startinr wcmllj 3qg92 ,+tp+wx 2fv0zg from rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 3p9,mft2rx+gwlqcz+ 0jvl2w m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If thx-:pzxa0 7ta ae average force of friction is equal ta:z7aa0x xt-p o one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/si:wx j7lt p() m l**okprs66kx reaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very c65i iu 7 x7git6pqnft5z)to1 light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is nozi i p76)ocn1t5uxfg t7i 5tq6ted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very liwko k9,e)4q/n0s+p jbfxl 7f fght horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, howe97bwxnfk0f,4o/) jkl pfq+ s far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mpe 5ar-w1gf4c ass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (1gwcpa5 -f4 rea) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sij ozz3p c+ (o8i bi)g18apsu2o;u e1fxxth-story window 16.0 m ausopof(c ;81io xa+ bzjz3u 12i ge8)pbove?    s

  If a car generates 18 h b,zp9 utp*7hd;b4 vmtp when traveling at a steady 88km/h what must be the averag;*9p 4zdbub, tvh tmp7e force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is the avera8,km04)-u wbjqyy oiige power deliveuo mw -yiy4j kqb80,)ired by the engine?$\approx$    hp

  (a) Show that one Brikks+ gp5m.bh5 tish horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the formwzx3a8;d4 a ugi2)uyc ur(y9u of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her jhg,:9lp:6dy8m b-p :jv( ia v pv7oki1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Ap ,-pvhmiv g78j:yplk :9(p6a: bdivojproximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp 5 s;ic/ ;h a58uhiwuin g:7 nfh-yy0j3toclf*motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter acceleratec8-u xg-(4y9d ajm7cptq0kyfwq)s5hw3 u (j os a 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power7mqcw 90 k-8u j4chj-wy)5 (3ya xtf g(ouqdsp was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minutxsvspojhvv :b(+4* ts: 9e3cuscmc-( e through a height of 3.60 m. What output rating (wattm:jsos e-hs3+(s (tv bv pxc9 cv*4:ucs) should the pump motor have?    W

  During a workout, the football pl g )ibb2i(1necayers at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an ang(ebg )i12inc ble of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0ty90rg lu)lu3 qrh8*l $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 127riqc0kv zv6/0 hp. How steep a hill can it climb at a co6 v7irv ckq/0znstant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepowjk) kye/97gk .l2rtot)0(9jaq cpdefer must a motor have to be able to drag a 310-kg box along a level floor at a speed fo)cq 92/r kdae t9jk)(.ljge0t7kp yof 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.vk:ihlm 4d. 1e0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8ky9sd*; ((q+d oi4b fyvzd2qaeb6 1(gt2 xdlvtm/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an ev6g(t l2xdiq *by4f(d (eoq;1s vad9 2yb t+dzlastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, an: 4ir(o tl/ierd the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to statl rri/:i(e o4rt? $\approx$    J

  A film of Jesse Owens’s famoug /cx4:j cz/pb j(pcn/rr gw+ ti)e/(us long jump (Fig. 6–42) in the 1936 Olympics shows thni bgx)//cg we: jjcpp4 +u zt(/c/rr(at his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding witifq vq9p0(yid7 )ni8*ddc95sv x (pgrhout friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the vdsq n99 r(pc0* p7qfgd 5yid(i)vxi8very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m 2vu) e.cme u d.b-w,uvafter jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate b.,uemu v-vc .de)2w u
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose, )lgjqb7p gn, other end is fixed (Fig. q ,lggjp) 7bn,6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top ofz5, u*w-w9i.qjd s bdg a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calcul-*dgwz,q5j .wubsi 9d ate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a 1y7/. n qbwlnr0h joa0huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California ohead07r)eiwo6 t20yaef 7e 5claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, esti6edor7yh 7iwt)5a002fea eoe mate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/;kp.f9++oxf7 ;c*vsa w(aa z xne,fbys and falls vertically 81 m before striking the turbine blades. Calculany9+ +v fsfxoa(z .*;a,kef; bcpxw a7te
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circulja4i rb u,9q :(;cao mj(xbu:q 9v0wesar vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as lo9 uq(9a v0wa qc;,roj bumj:( xiseb:4ng as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, how highv om(hdpo( fitq)n) +6aglj)4 could an 82-kg man climb a ladder if he were fueled by one bar (=vqmo d6i))fah(n )jg+o(pl t41000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 4l3gr2 e5+j5c .hcciqw 5.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, 1guj/0 sm/8z4uwr khjtool;gn+/og*;v0 yao the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on 8k/ 0l nog4w//+ooaj0hy js*gt; ;m1ru z vuogthe scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, ay rj,yq( n(a3pnd swings out over a lake (Fig. 6–45). He releases the rope ,yjqapy3nr((when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance ofvafcgwani;767-d zh. 5.0 m in 9.0 s. What minimum power output was used to accoh7n. a viw-a7 d6fzcg;mplish this feat?    W

  Some electric-power commt7 xfmv/1j l8xn61rwpanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 1 /wx8x l76tr1mjf1mvn20-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffnem6y hct kyo1oa(8v0i ;ss constant k is cut in half. What is the spring stiffness constant for each o; mvyyc86i(1 atoho0k f the two resulting springs?   k

  A 6.0-kg block is pushe*cl q)2er0 m9ktsi0zcd 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how e ra,bln i5cg27,r82 yh1zv dslong will it take to accelerlrdbrays7 v ,n,ec8gi51hz 22ate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac funttnu6f6f3m afu0 enf5px9:q( ction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when (f0u9na equtmtff 36xn6 5pf: the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of phbh. p nyfpq f+o3r*t5-jp:v ;5z:q p500 m, what was its velocity when it left the volcano? fph5pf5-*p.q+jp v q:z y ph:3n robt; $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a wat8 b 5ay 05e*ej 0xpqikeq7tcr;er wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set ubxy0* ;rei57e8 kqq 5jc 0atpep to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s