In what ways is the word “work” as used ;5 vqlb8oy wlznt2x6k:zi; 9hin everyday language the same as that defined in lnxq wy5o:bzh;zv tk 8;92li6 physics? In what ways is it different? Give examples of both.

Can a centripetal force6n ktzxy55i .hsj n6(pbc-fy0 ever do work on an object? Explain.

Can the normal force on3qgskl21)() ghuiko r an object ever do work? Explain.

A woman swimming upstream is not moving with respect to the shoredv;: ug4lqsg7 u5alt5 . Is she doing any work? If she stops swimming and mel:a5sd 7tuug5v q;lg 4rely floats, is work done on her?

Is the work done by kinetic friction forry*lp emj*4 5cces always negative? [Hint: Consider what happe 54l*rjemyc*pns to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against 3yio h/ f1,bzma solid wall even though you are doing no bh31z/myof, i work?

You have two springs that are identical except that spring l is stiffer thrnlta41t; wwj7 13wvm5mtqu8an sprw t 71n jmr5av3;8l4wmuttw1qing 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 blovl 4m 4pz m tk1q+7re/ yuls2kt(8nm:p,o1ncgck that is free to slide on a frictionlesn1lpc+4 28mg4z 7 /:l1o( yrkqm tmsnp vtkue,s surface (Fig.6-30). The block starts from rest 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 poten8fu3yfj9s p ,dfd,8*hr w rlk4tial energy change when you jump as high as you l3,r y8f,ddw4pu*f8s 9jrh kfcan?

In Fig. 6–31, water balloons are tossed from the roof o-s p g/diq6k)hf a building, all with the same speed but with different launch angles. Which one has the highest speed o/g -sp6)qi hkdn impact? Ignore air resistance.

A pendulum is launched k ;y8bqci j(krrv+g(0o5i ;c yfrom a point that 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 second launch5(8g ;vj cbc0 i(oq+rykki;yr 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 uprisqe-m,lad+)w/ a6l yq ght on a table. If you compress the spring by pressing down with your hand and then release it,d-s, )+mqaqeaw 6lyl/ can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the c y-i/o:d5bew teiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the o-t/wyibd e5:ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when watfqf*r z:aoe7 7er at the top of a waterfall falls to :7*z7fe ro afqthe pool below?

Describe the energy tra2 vf.ru:vmai5 nsformations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a sko,ji3tc x*5up ier starts skiing down a hillpju5tx ic *3,o, but after a time is brought to rest by striking a snowdrift.

A child on a sled (t2sgc,8fo:9mdnc 0 cuqu3;cgc)l 2alfotal mass m) starts from 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) it is icm:n 9 )gsc3d;2 ,u82 qff0occluacclgy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their patfwzp :.ks 07votlcj,,bs,-brh rather than stepping on top bc o:7,pwsv,sfb k.zrtjl0 -,and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired into a ba-6txsg) 8jbmjle of hay. Assuming the hay exerts a constant jjt) s bgm6x-8frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinginp 7h5hmpg 0loh;5zuo f )ws5k7g pendulum in terms of energy, (a) ignoring friction, and (b) taking fp55ol ;h)07 pfmo5hk7gwzsuh riction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a -45j8acq+c b6u phsc cheight greater than its original height? 4j cbqhuc6p c5c8-as+Explain.

Suppose you lift a suitcase from the floor to a table. Thyig/mitra18 j 0l2 r/ce work you do on the suitcase depe/yciil 8gt2mrr j/1 0ands 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 table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather t pi*3b uu3np6c1c1pk,a vq7oahan the work.

Why is it easier to climb a mountain via a zigzaj+hy j ia+nh,:g trail than to climb straight up?+hn: ,hj jiay+

Recall from Chapter 4, Example 4–14, thxqoc8up4r63 /ddoba, at you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. c4/orpu, oa6dd38 qxb 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when azu)jv9 mxd,vb85-f-qbshbs+, *ivu d 265-kg pile driver falls 2.80 m?8b d +uqz9b-mhfv5 bdxv,)suj,is-*v    J

  A 65.0-kg firefighter climbs a fgx9j 06jv z-bklight of stairs 20.0 m high. How much work is require0zxjkg 9jv -6bd?    J

  A 1300-N crate rests on the floor. How much work is required to move it a -vc qher(rg 2h3aqz9k/xk (j,t constant r h(kxeq g-( ,qak3hvz2/r9jcspeed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) push9ad q(d:8 iplaing a 160-kg crate 10.3 m across a rd:p (q9lad 8iaough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a fxo8b5s4 -tkocorce across a floor at a rate of for 7.0 s. Findob4o kt sx5-8c the net work done on the box.   J

  Eight books, each 4.3dr*rl70l i8cl cm thick with mass 1.7 kg, lie flat on a table. How much work is required to stack them7lrcld8 i0r*l one on top of another?    J

A lever such as that showv-bbst0)ui v s/p(+pen in Fig. 6-35 can be used to liff objects we might not otherwise be b0vb )s/ epst- p+vu(iable 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 m down a 28° incli/s 9fj6d2 fn2/mzk0r pwgv2wha. t gx;ne and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic frictionpnzm2v ; f22hdf js6wk0wggx.r9t/a / 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 /wvq eer:b 9+ba helicopter of mass M an acceleration of 0.10 eqb+b:9 ewrv/g upward.    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 and thatoz 7i::n1agbs $d_{\mathrm{A}}=10.0$ 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 as shownc c kg/z8kk38v7+d onvx8gfm3 in Fig. 6–37. Determine the work done by this f8 ozcx8g kg3 knm/cf8d+ v73kvorce 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 acts in thg c+y3 qm bxd,zfw;6f/e $+x$ 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 molar876bi db vwu6 o33koecule, 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 what factor has t xid 5g*w4acnc a0n dv- -o k06(n(wk*vdszl5its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elec,1o(knsq dqsn23 kk ,9;pxo fctron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 t ils,t8b- z6f38rxrx f6m59)hu emjvk o stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow wh6 reif*7 d;5y m3ur86aokswhtose string exerts an average force of 110 N on the a6h dmw3keuf5s;8 t7oayr*6ri rrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s :*j* dr. kknugglove backward 25 cm when the ball is caught. What was the averagn:gj .* kkr*ude force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will itsxp k s9-a.0,nt630 a)dic o tcj9bobcp minimum braking distance be increased, assuming all else is the same? Igb)ik npt0x,c-p. b6 dt9c oaja3osc90 nore the driver’s reaction time.

  At an accident scene on a level road, investigators bdfy8v+- o(ao3*tfqfmeasure a car’s skid mark to be 88 m long. The accident occq b df-f3(f+v o8oayt*urred 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 locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kfs2jt rh( ) lkh1rgr57qo;v w+qf0 fa1g is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between thefsrwv;5 jqfro h7k+ l0hg( 1a)f2 qt1r plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg roccib2rok 0, .nok go if thrown straight up by someone who does 80.0 J of work on it? Neglect air resistancri n .b2ko0oc,e.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by8k 4rwe+x;n rl a single cable. Determine rw r4xn ;l8e+k
(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 constant, k, of 440N/m How much must 1aw2o.wxb- aw*as;tt this spring be stretched . w*2aax;t o1s w-btawto store 25 J of potential energy?    m

  A 7.0-kg monkey swings q.l5exh+aqdks ;k,;lxue ih: wmd*k1 rd, *6zfrom one branch to another 1.2 m higher. What is the change in h,1+ku*x*xka :eil zd d qd kwhq5rsl.,m6e;;potential energy?    J

  By how much does the gravitational potentiat yv5;k/bi/q7lb g; nkl energy of a 64-kg pole vaulter change if his centen 7 v kytbl5g/i;;k/bqr of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surfg;c 4no)o.9j ey9d.glo4 t yjrace has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 .g .9djytn 9ro4 eoj;4ycgo)l 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 groun ng1k+bf ib80nd so it is 2.20 m above the ground. What is the potentiabk0n fgni1+b8 l energy of 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 elevationktki80g :9 rxn of 1600 m and climbs to the top of a 3300-m pgnr9:k 08x itkeak.
(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 verticazof*mxoq 5* +nrag/ ;tlly next to a ruler. The end of the spring is next to t /otrfnazq* +mgx;*5o he 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 Tarzan, is running at top speed (5.3m/s) 7+ q/kcfry4: ewav .wgand grabs a vine hanging vertically from w4/ w.gv: ry7e+afk qca tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting8 4i)o)yfo zge wpn,j0 from rest, slides down a 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 given a shove up a frictionldm ,p) ub k*(d9apd0awj/dub 0ess 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 energy is transformed into graxp lw jejr- 06,dlf2lc,qr1snr ,++gdvitational potential energy without the aid dgqsnrr+f,dl j ec2w0,j ,lr16xl- +pof a pole. With what minimum speed 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 verwgp8xsyuzw.:: k8a, etically upward from the top of a platform with a speed of 5.0 m/s. (: ks:w 8za,.p ewug8yx$\alpha)$ 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 (ignore its mass), whose spring stiffne u saqp8a:w(;w,:xcwk ss constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed cka:aq x8sw, p;w(wuc:an 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 looped track shown in c y9ouyz6(2xh4+mamza( w8ua Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h(wzy+x4a z2y mu8aamuh(oc69 must it be released?    r

A block of mass m is attached to the end oxjaz3: w8qv b:z r9tb3/*jz 6.xwnuoqf a spring (spring stiffness constant k), Fig. 6–40. The block is given an inz:: b9junz.xq/o vxzwba63wrqj 3* t8 itial 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 bridge. She is tied to a.xfe hu5dx xl f(r10b56 0lpfg bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s5r ux61lbx (.xh00efpl5dffg law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–4 mefqoq o-w3w45w328jh kglm5 1 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the speedmj2lkg4mw3 wwoqqo5 3 hf58 -e at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 veocn r;3c* )vcjnh1*m/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 the bottom of an elevatgo9 u/ n7b7(,bk jhlfcor shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k shouldkhc(j7o n,9/7ufl gbb 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 cyooes,d1),dr c3lm duz.8:vlccle 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 kg and traveling 95km/h in opposite direc4y.p*e6zdyw- s. kwhx tions, w4y-dkz.p6. ewyxh s*collide head-on and 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 yr :rfp7p:bk0a speed of 2.2m/s Hok:ybprf r0p7:w much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slidehgssx ioa7rqc594 6+rs 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 tree 13.0 m above the gruvb ( hv576txg13xxlzound.
(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 ofg.6oy o3-ve qhdyw0z50 vhh:x 2.0 m, and it bounces back to a height of 1.5 m3006 g -y :dzwxvvh.hohy5oeq.
(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, starting from rest, is pulled across a flookhr* u. aj;sj+r with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of frictionu h kj.*ra;s+j is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes poi .zl yhp69fpjibm+ee+3 *+zqi4qpt :mnt 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed wil+4 :yfl3me 6ezp. qqmpjipib t+*+hz9l it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/5rs-cpox j9 ;xs 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 at g55sl*b o0k9med rns1tached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the eqs9g sl0d 51n5brekm* ouilibrium 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 attachd;+dc:t 6ejo aed to a very light horizontal spring, Fig. 6–40. The block can slide along a tatea ;c6do:j+dble 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, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttf uei8v7t;n+(tkulbbx p2 9 *xle used a “glider” (mass 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 (a)*8bv(eu7fntui 9k +tlbxx ; 2p 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-kgi v;sp;fxq t0 n56 5+mp a-y9kz3witjj piano to a sixth-story window 16.0 m i9 wxfv+3a n;p5i;y mk6s5tzjpjq 0t -above?    s

  If a car generates 18 hp when traveling at a steady 88km2)oz jinbjb l*m(,eq+x zyh+r- kp* 36pr kip6/h what must be the average force exerted on the3mj p-6 6yr)lnj2+p(o*k b*iik,ezhxz +prqb car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest townq vz9d+( uolt/cq0v9 )fw x/ 95km/h in 7.4 s. What is the average power delivered by the engine zd /fv9un9qw)tx0cqwv +l (o/?$\approx$    hp

  (a) Show that one Britis+q/nuf( kc .ich 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 0)1e44quphwxg u 4ykeform 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 hdqtt30y8yh*wh.j+v m3aga f fh0 6k -rer 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power kwfyjaa6v hmd030ht-* rqf8 gh+.ty 3(watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motp4 l*sqo t.2x;bzap 2sivp,7x or do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this u(kob3v*,d ;;hmpgnx motion takes 1.5 s, what average power was develb(pkhm 3og, nxv;*ud ;oped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute u0g9t*rjt a7m.+ y6bo fjj: r,5ropgb through a height of 3.60 m. What output fbj 76or o.y5p t:*9rj0t jmrg,g+bau rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the st saua :ky(tqv2 jg69t i22 5yy8jay2szadium stairs in 66 s. The stairs are 140 m long and ii2aj 52(96 yauszqyv2atyk: 2g8ysj tnclined at an angle 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 xqq +dy; 9:1s4,ftzoxjc5obs* u uk6q 6.0 $^{\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 d 3dx::rmwk,n120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forr x: nd:,kwdm3ces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box oe s ( c6g;:ohv26evrpalong a level floor at a speed of 1.2m/s if to 6(pvrc :h2eg;o6sve he coefficient of friction is 0.45?    hp

  A bicyclist coasts down a w1xt; gygdy2q cu6ix20q7+ l w7.0 $^{\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(8km/h) bumpera4(huk 5)w:ppeyal /ceu. 2gss” that are designed to co/gu. 4kplaacsw5) :pey u(2h empress 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 elastic 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 th,simgyxkx*1+uu. .ihd xq10 oe ground, and 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 flo yu 1,gsxi umi*xxo01dkq ..h+or to start? $\approx$    J

  A film of Jesse Owens’s famous long jua.wd+v - hl3s h w:cu7jtv tqo)c9ca,4mp (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of 3t cohhl79a.4qu) jdavws+, :tcwv- c 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 i ;wm:/ +qnf-tv6e /inhrr/trsliding without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the /tn-h6nrr m v+/qii:tw re/;fvery 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 mj f *ou,sbr sl *,do6or5u:me* after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1*sldf jo o *b,se*,5:umou6rr.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
(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 otheif ;y;;bv5i-ennqd e/ r end is fixed (Fig. 6–43eifn/bni5d ;ve;-; q y).
(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 of a 3700-m-hie pkep 5k/g-6lgh mountain. The climb is made in 5.0 h starting at klep5 p 6/kg-ean elevation of 2300 m. Calculate
(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 breaksoyzo2f21kqz: ri w8 ,hedks4, when a 920-kg elevator is 28 m above a huge 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 claims that its lifts can mov wk)(ytvlxwcdvli4;d 9(5- butj04 t he 47,000 people per hour. If the average lift carries people about 200 jb4(ldvxkhtw(yut9dv4; )w0ci5- l tm (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verta;n:m:p uol 2xically 81 m before striking the turbine blades. Calca2x ;n:l moup:ulate
(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 circular vertical loop (Fig. 6–44), th1uj/bpr0vp t3wd.3z me difference in your apparent weight at the top of the circ 0bp33ut/1p z mdwvrj.ular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long 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 cafl8wl8 0t3jwg lao(- hndy bar directly into work, how high could an 82-kg man climb a ladder if he were ojf8(ah ll0w-wl3tg 8fueled by one bar (=1000kJ)    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 jv ws(2/s9aa t0b z3rw45.0$^{\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, the qte+u/)r s /bezcqo6.spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the s).zt/ rue6e/oc+qq b 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, and swings cz dt/2ccs h+yx;2w *iout over a lake (Fig. 6–45). He releases the rope when his velocity z+dyccc2ws/i*;th 2x 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 of 5.0 utp, lir y 4 .brah,;2mzswu.2m in 9.0 s. What minimum power output was used to2stp;y4bl2h ma. uzu,i,r r.w accomplish this feat?    W

  Some electric-power companies use water to store , z r)wg/4u yqqj-(ikpenergy. Water is pumped by reverrk)wpi4yqq/(,gj-zu sible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-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 stiffness constat hk m3yy1;3fz-i-dj-wu ng; vnt k is cut in half. What is the spring stiffness constan wiyg-kztmu h- vy-d3;;fnj 13t for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a roz: )zti4h ro+gugh 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 acct7jr mx;- efx:ktsd- .elerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelere:m;t d ksrxjft7.-- xate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”),r 8 xr-ki8rt;e the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping trxkir8e;r-8 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 dist7j6-grq uxr5 2tia 0fvr dyj(0ance of 500 m, what was it fyjrv- 05a ( t6r0qd2irujx7gs velocity when it left the volcano? $\approx$    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 water wheelp:m0rfbc 109zgghf y1 from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set yrgc9z1bpm0 gf:fh10up 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