In what ways is the word “work” as used in every(2h z4 b;saszfday language the same as that defined in physics? In what ways is it different? Give examplesh z; (zs2fa4bs of both.

Can a centripetal force ever do ge zi, 0-s.:axap -8zexq4khqwork on an object? Explain.

Can the normal force on an object ever do ui, ;ol hp1c*e6x9maqwork? Explain.

A woman swimming upstream is not moving with respect to the shore. Isi h8or)x1)v uez*mvhh)mjh.9 she doing any work? If she stops swimming and merely floo1)r9evjh)i u8m)zvhh mh.* x ats, is work done on her?

Is the work done by kinetic friction forces always negativewlw ,2,-g *s hzwmp)eu? [Hint: Consider what happens to the dishes when you pullh-m w2, ww,szgepu )l* a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though yh51 1iisvg(j zou are doing no woi(s1 hv jzi15grk?

You have two springs that are identical except that spring l ieslel zr mw6(q03j d0/s stiffer than spr6 /(lzw30 ljm0eedq rsing 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 thatqad (2*hck m,k is free to slide on a frictionless surface (Fig.6-30). The block starts from rest ad,*mc (q 2kkhat 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 energy c3 ;dnpcen y-,0078wof jwbgad wda2j3hange when you jump as a cy3d2bnf g-08dapjed3o ww70,;w jn high as you can?

In Fig. 6–31, water balloons are tossed from the roof ofke5wn.nno2 z *ui6md/ a building, all with the same speed but with different launch angles. Which one haimd6z. n/*2nwoukn e5s the highest speed on impact? Ignore air resistance.

A pendulum is launched frot vbcc,ao-9tw )7q )8fpfw na5m 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 launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position?tf9)facavpt w 7-o)5w b,8cnq Explain.

A coil spring of mass m rests upright on a table.fc9;a;klum o+ If you compress the spring by pressing down with your hand and then relauco9f;m;k l+ ease it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The instrucqo l/:a64z9 dmvqvtw0tor pulls the ball back and stands against zm 0qo6vvw4/lqa9: dt the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitationalu z73 60x9xsbohw c0vf potential energy when water at the top of a waterfallw70fobu6cx9 xv 3s0zh falls to the pool below?

Describe the energy transformations when a chilqzu2)8ax:nnti 0*v dc.b xlee 5.ax1 ed hops around on a pogo stick.

Describe the energy transformatioq/-bhz i gl;y;onn /7yns that take place when a skier starts skiing down a hill, but after a tio-yhb;i / z/;7ynq lngme is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a * lhdsxy /44lfgye *8mhill of height h and slides down. Does the velocity at gysl8fm4e/ yhxld**4the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fw n4.0.u:f9u)ozv /k/t.ny zqgoc oojallen log in their path rather than stepping on top f0vc/nqkjoun.zot u.wz4 g.y /)o9 :oand jumping down on the other side. Explain.

Two identical arrows, one with twice the speed oyluay upe0dx-j y:w157c ydyb7 4l/e6at+ 4m if the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow ij xy +7bpuwtu4a- 4 /0cy6eyymy5la:d1 ld 7ewill penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simpns yyd3jkjiba ua-5g 844 1hw/le swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a gran ab-g4ay/i85jjskdn h1y u4w3dfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than itgm1)2xc*pkp0qf0 h9j+ mj ilxw+)* c*rh eoovs original height? Explain+ hjxo) m9 k +mw2r*c ehj)p0cil0vpf* 1xgoq*.

Suppose you lift a suitcase from the floor tor (xrdyv yf-,2 d4zz5r a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straightv -z54xdrdy f,yr2(zr 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 theq e(qxiu8vl8d)e5 c4r power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb straight u 8:rxm)2y k k bvf,iw,hcn(;rup 8yi)2 nxukr m vf(h;bwkc,,r:?

Recall from Chapter 4, Example 4–14, that yr2hpneb0 eqw o5s9 1o(ou can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is ra 9h( bsp 5eenwo1o20qrised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational;m m/k vv ryzrl61o 2xtun1:0n force when a 265-kg pile driver falls 2.80z:vymkn1 v/;rxut ro2l6 m1n 0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work is relw+e4s tr2m: 58ih zttquir+m:r iwh82telz4 tts5ed?    J

  A 1300-N crate rests on the floor. How r4v,y4 mowt8w much work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of ,o tvw 44m8rwy230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontallyfbqvdd1s .d n3ad*u) -n4hih0sz-k1b) pushing a 160-kg crate 10.3 m across a rough floor without acceleration.34d1d1nh-hzi)du sbab*sn0 dq vfk- , if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelenn6l l08o/xbu rated by a force across a floor at a rate of for l /n06ux lb8on7.0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie fla * jot y;l4kqudcpkg q cy0b4;p5pn.(8t on a table. How much work is required to stack them one onkk.* 84 ( py5o;cd4 npjy utgpbq0;clq top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we mighta.ot)ux.g uz/mdo)a9 not otherwise be able to liff. Show that the ratio of outp)9tu . ax)o /mgduazo.ut 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 msn+s f/7y x1cz down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effectives nz1c7x fy/+s 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 anwlw)0x7mx hu; acceleration of 0.wlxmhw0x ;)7u10 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 that p/q f)2ez252kbz7habey5mh a $d_{\mathrm{A}}=10.0$ 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 shown in Fig. 6/o54 v0uftu4pasamkd12 8t iz–37. Determine the work done by this force to move ts fp mztu/442auk 8o1 dat5vi0he 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 exertepay9szvj ; .+x)mzyk) d on a particle acts 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 molecule, with mass ouep:lc;,yzro u(v*p9f $5.31\times10^{-26}$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 ar2x/gauh5lj h(+ l y -3fkkjw(frow is doubled, by what 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 required to stop an electron kttj19+ 80cu/i1wq i0mv hplv$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 194h*gr-rkw ko0z lq0m h 4v ,iw)wq,um250-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 pn.z6cei. ,pf)b ske3zpk;+ nof 110 N on the arr.3fkp n+ks n) b,pe;zz ep6.ciow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelin4 z/z k-y1 iw8sdhgsk;g 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the glove? igs-4;8syzw1kd hz/k    N

If the speed of a car is increased by 50%, by whah(pry 0qrkn g6.qwi69t factor will its minimum brakingh k6 nwq(r9qr6g y.pi0 distance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators mets5rbxyxz ,hc(y,)v: asure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction wa, yz(tx)y,5rb c: vxshs 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 kg is pitched at By the :/ v8+ rbfs4bduzsqfelr 7 )y6skfh; 5time it reaches the plate, it may ha ;frsl4 fd 68uy sk5hbs 7beqvr)+f:/zve 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 thrown straight up b3khoy; n*6bzz 0 f0exby someone who does 80.0 J of work on it? Neglect a03hf6*;bzzyebo0n k xir resistance.    m

  A 285-kg load is lifted 22.0 m vertic k3+/ghiomna gv+a yf3 ,jk+sg8b6t1bally with an acceleration by a single caboaig3,y86+ ng3jabhv/s 1bgkf t k++mle. Determine
(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 mtp.a b.j.w nl5oxv./ grw6vkq/ zr,f3uch must this spring .rv xwra/g6jpn3 .wblq vzok.f/,t. 5be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What bi0fex43pkd90 n 3wgzcs2jr8hd 1x*y is the change in potents93kfzd 3n *2h4dx1bx 800cpgj weir yial energy?    J

  By how much does the gravitational potential energy 0cdf uh tyzfg ;ywz2h218*m1 uof a 64-kg pole vaulter change 1y18f2zhymz h *;0u fcwd 2gutif his center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizonta +-x.vr dk 1uoz7 sn,w8c3ssb-wow; val surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is br8- swvockn xow+ 1wsdr;ba.z3,s 7v-uought to rest 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 2t wjwhgb6 z+ke *v8:u(.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the8utewj +gbv:6kh z*(w 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 ag 0xwwt b28z3yg9t h2c)dp9xdnd climbs to the top of a 3300-m pegpzxxgt9dyc 9t 0 hwb w)38d22ak.
(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 vertic*12op) .n opt ekf6pxwally next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of thefx.kte 21o*p)6p wp on spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3f3p u:..n5)c):y x sln*exgry5sxz u nm/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high ca.s p5l xu:egu):3fnr sy *y zxn5c.)xnn she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides dowz umstmk e ;we.(s70k)q o.5rwn 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 frictionless 28.0bq*:ovun+ yw,$^{\circ}$ 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 6hnkxt2-06k 2ti dk1xdpp 6b9s g5ttj is transformed into gravitational potential energy without the aid of a p xp5tj6tkph1 gkdx290 bitd66- 2n sktole. 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 vertically upward fro l 12rmf566ylj d3gdwom the top of a platform with a speed of 5.0o 366gfyr215lwl djmd 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 (ignore its mass), whose spring stiffness constant isyx q9i .:vl+hwo* hfc6 950N/m is attached to a table and is compcxhiw lvf. 9q*o +:y6hressed 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 wijhhdn-y;m8po8 *ss3p thout friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, evenmp88 j3h;*hso s-d ypn 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 to the end of a spring (rrkb cn(xkg2 w.8 u*x;spring stiffness constant k), Fig. 6–40. The block is given an initial rkkxc*xr;bun w(8 .g2displacement $x_0$ 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 tz vt ps0z o0z1mistb7uz2: fc;yl4(9ko a 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, assu pm zz47yo;9f (bt k zul1:sc0i2vzt0sming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car sh1/5*op. xqitptg jov /own in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the spe g/1ojvtppqiot*5 /.x ed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed3rpm g w ;,ivtl f6: w)a;4vzn0v0+hazhqi hv3 of 12 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 the9lm0/vzdvj ;8ay 2q/ kwttr* s bottom of an elevator 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 should have dlvm qy av92kr;tt0/jzs *w/ 8so 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 cy-.vx 1-vi eblk3wjy;m cle 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 itw mk-r **9cbp3a 4rtzn opposite directions, collide head-on and come to rest. How much thermal energy is produced in this m3tzta* k 9bcrr-p*4wcollision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the botvj/m xx hz(- :f4nf(n5gx m*x;kk 6zlotom with a speed of 2.2m/s Hfjzg v6o5 l -(:*kxnfm kxx;(n4mhxz/ow much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides down a 22 1u:.a o :5japv;vz9z8psb tpw$^{\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 thev5bg.ji5eman1ve -( v 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 7ado1tzg: e8 iheight of 1.5 md8iat1 7e:oz g.
(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 fr kdq6+(ajwp0r*dvrgk 2 or3:xom 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 *aj60rrdvxo (pk:k r 2+d3wqgnext 15 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 withu 3jrq 95o29l bg:yt p.attfw8 a speed of If the average force of friction is equal to one-fifth of its weight35tfr:8 tpot2ylw 9u g9aq b.j, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reache4: gtrwj5u0 /jrngcu 2 uar(8cs 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 light horizontalf tl 13ytd0l5a 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 equilibrium position before stopping aa 1f dtyllt503nd 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 light horizghv( 6).haur montal 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, how far beyond its equilibrium position will it stretch on its first swingh v)hg6raum. (?    m

  Early test flights for the space shuttlea8e 5j ht7(vb()manf k 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 tem bhkv(n a8(f7ja5)speed of 200km/h (a) 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 +mfmo9lm.cz53 am pt 2a sixth-story window 16.0 m above?5o lm+fa mm29pt3 zmc.    s

  If a car generates 18 hp when traveling at a steady 88km/h what must , aeva5i xio,loo 59b3be the average force exert,ebi 5 va5oxi,o3l9oa ed on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from res8o(kguwd8 ih0tu9j1 ft to 95km/h in 7.4 s. What is the average po( igfu1 t8h8uj9kwdo0wer delivered by the engine?$\approx$    hp

  (a) Show that one British 7e+x2jkxksievl1p jpq* z8t+q0. b8 nhorsepower$ \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 unitsm s./;) 6jd(nrqezwu)og uq2 p are often expressed in the form 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 1150-kg car slofattgge9- 2bn +k3(8qb, vnp vws down from to 65km/h in about 6.0 s on the level when it is in neutral. Approxi+v fa28bvt3 ne-,g(t 9pkb qngmately 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-h18 (xb,jshj xcp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot zlu b,y+gh:pov9 3j,kfrom rest to 14m/s If this motion takes 1.5 s, what average powe:vu,,jbo9 pyk3hz+ l gr was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.n /84rov*n mi.sz7zsi60 m. What output rating (watts) should the pum z/84mn7ni *i .srvzsop motor have?    W

  During a workout, the football players at State U. ran up th6r5u5rceti m02zy meo( v4bs9 e stadium stairs in 66 s. The stairs are 140 m long and inci4cm r5erues50 (yv zom 96bt2lined 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 cycli8bd9lu6q m d)n(hsq)g st climb a 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 ob wr8dcq; tw+f3v2k *mgjt,g9 cs*e;g f 120 hp. How steep a hill can it climb at a constant speed of+ gbqw*wc9cg,tk ts*jeg2r 83d;m;v f 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 3z h y/c teu3rna)sp.n:lg4 f4*f5v9aq10-kg box along a level floor at a speed of 9r./lnp3zya 4*ac sneg f:54tuq) f vh1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dorw d ud5onp(8..h2 agown a 7.0 $^{\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 “5m. r ky+p pgy7o:*le; p*dvvl:qi/h(8km/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 perma7kge lp lypqv.+d:: ; ov*pyr*nently 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 the ground, and the remai(d7/pl: s8yfr y) bv j;b2ffjmning 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, f8yfm(; ypj d/vsf 2jb)l:7rbhow much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1r, nq 1xz5v)hrzqj0bce;2p v 5936 Olympics shows that 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 w)r1qzz0bvx5jcen2,rhv; p q5 as traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track s alh vvp1 x4e*0-cp9mbhown in Fig. 6–39 is to remain on the track at all times, even at the velpc hvxb1 9*vm-pae04ry 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 mx6z /)gpp* xoc after 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 hiopcgxp/x 6z* )s 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 letg ;i0:c)z i( xu2w8pavuy(b wngth L whose other end is fixed (Fi(bu0 w)g zic2vyiupxa( 8 wt;:g. 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 of a 37004f3bvsf;n 5k9su* rp +7n tnll-m-high mountain. The climb is made in 5.0 h starting at anf r+l34k; fvnus5ln s*b n9t7p 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 breaks when a 920-kg elevator is 28 m above a huge spring (:)b. bv3/bon p kq4rny$k=2.2\times10^{5} \mathrm{N/m}$) 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 ed; vm;xhyg-g9s5i h,9kvep 9 its lifts can move 47,000 people per hour. If the aver v9v9;h;ggky5ex i9es-d,ph mage lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam p2u c vnx7y/qirr2v1-nq y+q9at the rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Calculat1nvq9iyc 2-72ux/r nrpyqvq +e
(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 circula(gpxk3/iprlb-)6d us r 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.p p6bdi)k-r( 3 u/sglx 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 cand93bfj 3s5hlcdb7yh t+y bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=f 3b7tyh5b3l+h 9csd j1000kJ)    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 anglevy6v 7bq +s,pl4irc;h of 45.0$^{\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 sprinz ,ia:euxcu ,+g inside the scale compresses 0.60 mm, a,caiuu,e+x : znd it tells you your weight is 710 N. Now if you jump on the 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,qoubfcfo) 002 and swings out over a lake (Fig. 6–45). He releases tcf2q of0)0oubhe rope 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 ve dxyvdm f -v.)a filcy5,:u::frtical distance of 5.0 m in 9.0 s. What minucyla,x.f vdf-ifv):my d::5 imum power output was used to accomplish this feat?    W

  Some electric-power companie08 p (pp.mofke7xq k9hs use water to store energy. Water is pumped by reversible turbine pumps from a low to a high resh ek(.pmk 0p97qfxpo8ervoir. 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 consta wcoqg3+ox t,*o,:5m+exse cynt k is cut in half. What is the spring stigc*eo tx+oqx+,: me 5y s,3wocffness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed gteu w(dsx( e*z),3s.bv3j bwe)tp q(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 long wi. bqg lf+t1q)s:)eki pll it take to accelerate from 55km/h to 75km/h Assume the power stays the :isgelt.kq )fp q1)b+ same, and neglect frictional losses.    s

  In a common test for cardiac function (the “vsuc6- 0rn+ odstress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patie6osu nc0+-dr vnt when 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 spewsbon;o)ugrt1 gwb692 r a 500-kg rock vertically upward a distance of 500 m, what was its velocity wn;w g r6b) 2t91rgobuohen 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 whr o lp;ohjhx2,; nbd1t89+o zheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is oozl,th1;+d j2rp9onxbhh ; 8set up 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