In what ways is the woluq48 ic +brxb1ew0 (+yi5aw8 ot*wnbd* 4sxrrd “work” as used in everyday language the same as that defined in physics? In what ways is it different? Give examplen +xai81eo0ww y d5uc4xrb ir*b (b4t+q8*wsls of both.

Can a centripetal force ever do work on an;:do4uasnim p eu 70t; object? Explain.

Can the normal force on an object ever do work?)h0 0lhqaaegp/( kipy8. xvr2 Explain.

A woman swimming upstream is not moving with: + c )u3qt9gwfv-gzec respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on heue:+q vcgtz f3) cwg9-r?

Is the work done by kinejdt , w.nl8 htt8gbw)9tic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tabltjt8wnw t)b .glh,89d ecloth out from under them.]

Why is it tiring to pusk 0qy,mfhes ot q3th.ft53siq7,ko; (h hard against a solid wall even though you are doing no work,otqq te k.yss0h k tqfo3ifm 35h7,;(?

You have two springs that are identical e2mjxzrs(q ) bte l)n6-xcept that spring l is stiffer than spri)2mqrt6e xs(-znjbl ) ng 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 forceu q 2ld mum3;ib swv3w)gb4;a9 on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has ts 3idbumw3; aq mvw9lu2) 4g;braveled 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 do h9uie48qcpaa 7+wof 4es your gravitational potential energy change when you jump ua+o w ec79pfai8h4q4as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all witaa 2cybg z9zn+5evc 5qq9w;/,wnv v-kh the same speed but with different launch angles. Which 2+9yqvnevn /9gaw5abwz qz ;,5-cv ckone has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height jivg*yn04yq3 u n+x2x 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 trajecto gqijn+4x0yuv2 x*n3y ry, 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? Explain.

A coil spring of mass m rests upright on a table. If you compress the spring 8ivff nn6kmop4 25 +*lwxad b6by pressing down with your hand and theok 82nmxbi6 + pwav46*dnl5f fn release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung cfd4sja29f .i from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release th.sj fcf9i2a 4de ball without pushing it. Why?

What happens to the gravitational potential exzgb .5szg 8aw90 zqq7nergy when water at the top of a waterfall falqabq 0 zggsz 75x9wz8.ls to the pool below?

Describe the energy transformations when a child hops around on a pbcsl.-;xh5xa+l,g g zo(4 zliogo stick.

Describe the energy transf-alv 9i nypaaoo7+b 0.ormations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking byo pa9n+ .7a-o0aivl a snowdrift.

A child on a sled (total mass m) starts from rest at s2 g- gxyt;2pr/h8it;1km bgx8vlf x/ the top of a hill of height h and slides down. Does the velocity at the bottom depend on th ; k8sx-8fyl1m2;t/xbpvigx2gt g r/he 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 fallen log in 5c+oj2nbe-c c their path rather than steppinbe cc+no5 j2-cg on top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of tl+1qxor(/h ;wvyjrxccb 5 c(, he other, are fired into a bale of hay. Assuming the hay exerts a constant f/o(c5;lc vy(xr+w, x bjhq1r crictional 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 70wil a+ o8(s gs1phztin terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfatherot8sp1+a(gsz7 l w0 ih clock has to be wound up.

When a “superball” is dropped, can it rebound to a heigh22 x0vksbi p sufxpf wutm)*,35g. vr0t greater than its original height?,5 f0ut gx* rvikpvpsm0u2)fsw b2x3. Explain.

Suppose you lift a suitcaslxdu ag,tw,; )e from the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it stra,wdg ;xu t,al)ight 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 pow/ o 7u b3qd6yo/7fjzg+e-mqrxer needed rather than the work.

Why is it easier to climb a mountain via5gf 1a6gpms3-+bdj+zvsxx0i a zigzag trail than to climb straight up?p+sd 1s+xvz0mj35 -fbg6xai g

Recall from Chapter 4, Example 4–14,)p2u arxf /*hwnz2xs jx 56l -tg5mo(z that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter th6hxw -n o *tx)f/5lj2as(25x p mzzurge load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravi3+ay:ivm9 w:o ir:fm s )4rp/e2fl crftational force when a 265-kg pile driver falls 2.80 m? vi:r:mf/y9scw4)p:a3m f e rif2o+ lr   J

  A 65.0-kg firefighter climbs 4 4kc0oqv37f(mm tr9(g twmcna flight of stairs 20.0 m high. How much work is requireck4( 93n(4 tmr wvmgoftcq 0m7d?    J

  A 1300-N crate rests on the floor. How much work is required rr, m d:8hbztdc)5gu*nd8rd1 oh; w.tto move it at constan5*c zdnm wu g:r ddd8,r h1;)ttbo8.hrt speed (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) pushing a 160-ls867c 8tyr 9 ob/zh5 rghk.mhkg crate 10.3 m across a rough floor without accemhchros r85tg9 .8k/zy l 67hbleration, if the 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 8u3lwjaa or- 24ul53gaybs q (rate of for 7.0 s. Finwjuly2b-as3 ol 54agr 83(u aqd the net work done on the box.   J

  Eight books, each 4.m,wqtjlpwff12 87vmw wj j+5/3 cm thick with mass 1.7 kg, lie flat on a table. How much work is required to stack thefjwwm 51f 2/wjjtmp,w v+7 8lqm one on top of another?    J

A lever such as that shown in Fig. 6-35 can be ,m pk.n3kriny-po-w/used to liff objects we might not otherwise be able to l.3 nw-m ppkro/-n,yk iiff. 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° incline and if ju bbtigb (agbx ((-nzx;)t)3k*v k3s kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculavi3u 3*t(zkb(fg)jx(b; bn k gx)-a btte:
(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 requiredy6s-z oqz(ze . to give a helicopter of mass M an acceleration of 0.1q( esz-z. 6yzo0 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 fe89 vdxd(6 :v m;e21ixxxeqjaxis is linear and 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 as shown in Fiz3 2nqc1s9a /c tb0qljg. 6–37. Determine the work done by this force to move the object /nq 12cs3cjqzt0ba9 l(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 parti(d. me(xpvxu1 cle 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,nz h2 9jngtk52vc:5n o f1fbr0 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, si/t8m 7cscf u 45.hzdby 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 elr3/r; ps b.;s wvsr.bjeeu63pp yd81k ectron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 1250-kgcar traveling at 105km/hlb(u 0v4d; ksq-d6.dbtee l k/?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whosehxzuptr *wgfdc5 4/i:ae ,m9 / string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed harpxfd/ceit9 wgz:u 54/ *,m of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travvku92mz e+xxz ar409y eling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted0z uy+xx k94 9ervz2am by the ball on the glove?    N

If the speed of a car is increas op ) 6v2ek/u4srmj inp4g2j8eed by 50%, by what factor will its minimum braking distance be increased, assuming all elspmr 8 ni426 jejvpeus4/)gok2e is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measqwm) 418n-vd)v bml naure 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 locked) the brakes. wqbv n4vlmm8d1)a ) n-(Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time ao*sij )3yz dy (0n3mpit reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance bd y3 (m3ij 0pzsnyo*)aetween the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who ,o elv 6mzt)3tdoes 80.0 J of worke6t tvom)z3,l on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration )gpkt wwvk9f:qsl 0km .8t/ 1k6c,iqcby a single cable. D6p8kt wcwq.1)qtc 9gv k/s0,kfi:kmletermine
(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 spring3e8s7yb9 drm d stiffness constant, k, of 440N/m How much must this spring be stretched to store 25 y8emr 3sd97db J of potential energy?    m

  A 7.0-kg monkey swings.cixo8m +e1 nc from one branch to another 1.2 m higher. What is the change in i 8 exmcno+.1cpotential energy?    J

  By how much does the gravitatiggy33vgnc/ v:woz ca* fwb6i zl 58w75onal potential energy of a 64-kg pole vaulter change if his center of mass ris35 vf/3nlg5* w ocy: w8zwgcia6vzgb7es about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whenepb/t(q k.hw8 it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffnehb /(8ekw.tp qss constant of the spring?    N/m

  A 1.60-m tall person)d8h m)jxb5*,avcry r lifts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book reladrh)mrbjxy*8 )v,c a5tive 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 1600p8ky or 9v8p3h m and climbs to the top of a 3300-m pe98pyvk83 hp orak.
(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 vertically next to a ruler. The e v8wdnqv:hhjq 7:fvc:7dxc,hl t13h6nd 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 the spring, where will the end of the spring l77 d:hlf : w: ,6 h1vnc3hqjdxqvvt8hcine up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) anoe: sm07ckdt :d grabs a vine hanging vertically from a tall tree in the jungle.edo7 :cs0mkt : How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting zfas)p/ta8 , ufrom 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 )c749pf n86i/aatqb+ryeg oda 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 energy is transformer;ie8 oxqu zxjp7z4.(d into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to ze.qjz7 rixu8po4x(; 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 arti9 d 7qv/vyow6il56 jbsst jumps vertically upward from the top of a platform with a spe 7 5iv 9s6jyq/olw6vbded 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 (ignore itsbh mf-m zi;e2,v svec(rt,f -9 mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed bv2f sm he m,r,9(e-zfvt;i -ccan 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 frgax;e3hf5 z ujc*pyvc;--q+viction along the looped track shown in Fig. 6–39. If the blof- v3apvx g;hqzc +j* e5y;-ucck is to remain on the track, 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 to the end of a sprink a(nf5eix-- 4gg4g nab j)uxb2(ie2dg (spring stiffness constant k), Fig. 6–40. The block is given an initial displacemeng (ibg(x jf2- degabaek)5n2ui 4-xn 4t $x_0$ 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 bungeesde xt:i6 xdo 6712qxs-bzbr1hjg 14 o cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate ths6 j6iqx1rx -17be:x gosb2ho1t4 dd ze spring stiffness constant 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 pointnh/1g m)hu( +no /w;iu.aowsj2-rbwf 1 where it is released from rest. Assuming no friction, calculate the speed at por1;uwws/mo -ih+n an) j (f.ouwb/h2g ints
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an angpg lflorb.t **wb)2 .csynp(-le 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 bbzsox p*ahpbt/ye2:ajf-* 3 0e placed at the 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 hayp*bhj*f:o t3e s2a-xz0/ pbave 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 up a 7.uy*:)3k+ p(fztq bonz8 $^{\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 mas+iw2zusec +se:r0 v .ps 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal en.wzvr + :0spc e2ise+uergy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high andqbtit29 x8jj4jm 0 5vm reaches the bottom with a speed of 2.2m/s How much thermal energy due to fri2m0jj5 b8i 9xtv4t jqmction was generated in this process?    J

  A ski starts from rest and yiy;j h+n)r9wslides 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 lt)yrh,:r 0. 74e rmcs yb2kaha tree 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 hei +yt *8;- cynq-hq+qece/fhi uv7tfxnw,m5- wght of 2.0 m, and it bounces back to a height of 1.5 m7n/ y t8w ix+ umec-q*thy-e-f,5+qnfv q;hwc.
(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 floor with a con*d dpyq- dj /r;o9o*ytstant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed ofo qy;dy pd-jo*r/td*9 the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speed of If thcjnrcy r ;+u5lgm*zy,b+mo;0e average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distc ;y* 0rbyc5glom j+num,rz;+ ance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s re3 zv/)) fskizhaches 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 horiefd7qm2t3a:6 aveuu2h atk 9 9zontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the bloctuuv: 3qa6 97emekd 2ftha a92k–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 light horx 6ae g.rn8 a19d,ptj7c1kpo jizontal 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 fr .p ,86 tajgjoepa11dk9x rn7com this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg k pd5c-cx1cbti7 zoh1ldo- + +including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed 1 d75o-bd z c c++ihkp1-oxlctat a 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 a sixth-sto57h6cwo/fg*tf. 3tth(rt ykq7 ra p)yry window 16.0 m ab)f rw.tqt/ky 6 ftt3o7* 5gr7cphh( yaove?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be thee(v*nsr .7(fbsq3a f s average force exerted on the car due to friction anqrs(. be(af s7nf *sv3d air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s.ur9l7 5 az.lgi What is the average polzl9g5 u.7 raiwer delivered by the engine?$\approx$    hp

  (a) Show that one British horsz;cms an:b6y* epower$ \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 form of “u1kv 96l1 lvwnkilowatt-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 slows down from t;g z)f gzghe.5o 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car travegezg;fhg 5. z)ling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor3:ewstq(ex :qew -(q+y+ vxm b 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 motion takes :*fuu3oae2/96b iqo 1 vo)aqtp rz0bv 1.z2b6ef/ u:0arip) 9u 1q t3vv*obo oaq5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a 4xckyo 6g)xj4height of 3.60 m. What output rating (watts) should t6 c4xxj 4ky)oghe pump motor have?    W

  During a workout, the football players at State U. ran up the sy)k6m7e6:8 g +sivmzs eh8nfktadium stairs in 66 s. The stairs are 140 m loki76he sgv8)z: m6sk+ nyem8fng and inclined 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 cyclizvg-h9,gq b*j 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 of 120 hp. How steep ash pgic5h)h2i bb7l7 0 hill can it climb at a constant speed of 75km/h if t b h)cb75gi2ilshph0 7he frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be abu8hh/2*pj0t jka4,m8p nyu mgle to drag a 310-kg box along a level mh8ua*8jpk /uy2thn pj4,m0 g floor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down anfw 2 aagybt6(d3etdkql:1 /6 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 “5mi/h(8km/h) bumpers” th34wik33l2x 6xlo py7apnm( * gth) yjlat 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 elastic spring up to that pm (7w33txx)ll*k6n o 43ai2y hlyjgp 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 gru- 3alclx sg8 /7 lg6czw77ldzsj 73leound, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has zwd- ls6x8ae3g7g 7uc7lz 37l/sjclla 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 start? $\approx$    J

  A film of Jesse Owens1u.9;)pzb1bo; c4 fes2k lorjcbsf ; x’s famous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch pointfo9;4;eu;o11sz)j2 brcfsl k bcpb.x 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 without friction along the 8+0fwvygn 9 ealooped track shown in Fig. 6–39 is tv 8g 9+e0fnaywo remain on the track at all times, even at the very 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 after jumping from an aircraft without his par) *e gs9 w3wdd )fq.yclm7xu;lachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the)d;l sy .g9dql c)uw* f3w7xme 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 oth8gt2ufor8ffkba w+f9; ob48ter end is fixed (Fig. 6–43).owob 94f+8f;8b kr 8 a2ftfgtu
(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-high mountain. The climb is made0:ru8t/ y ti*l;qcn6tmwsd0 )cwwub0 in 5.0 h starting at an elevation of 23:i u) 0w6l*8wyt;0s0c qumw/t dcbtnr 00 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 abop -x8/fm/p:ees 6zb j7b ,hro1 v:jrbeve 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 move 47,04oyuecb.6xp 2gct qi r(m -06w00 people per hour. If the average lift carries people ab(42t qiryeg0 c-6.mux pw ob6cout 200 m (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 vertically 81 m bunmyhk ohe )-l7n ,/ ofz2l99cefore striking the turbine blades. Calcu9o7ez nyhh-l fo9mku)n2l /,clate
(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)iq 8- enw.1 9)zesuwpfz9/qh p, 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 lonq- ne s9wwfp)/pez h9qzu1.i8g 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 candqsbf;8o20i mnd,t 7 fdy bar directly into work, how high could an 82-kg maf7f,s d8mqd b0 2i;ontn climb a ladder if he were fueled 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 upwai +s5xlsyp;.(t aa5gfrd angle 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 spring insivs yi0(.q8 dqm p mal9joon5/:de the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now9ilvs0( . a5opy qmoq8mdjn/: 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 r5fp y. /0yugc:gukxj0kg: 2f 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases t fcf:g0y:2.kugj0x r5/ukgy p he 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 athletk -i u)-dyt*.nuay0opp/ ;d foe climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this -tuukydy;p a0*o/p )o.df-infeat?    W

  Some electric-power companies use web;b0z/ riug h8dl di7uuz2pw,,/j: dater to store energy. Water is pumped by reversible turbine pumps from a low to a high resdg2 ,,i8;p: jubd/udzrw eub/zli h07ervoir. 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 constant k is cut in half. What is ths-xx-ayx7 e (p3xrwmat 96 7rue spring stiffness consare7tu 9-x3a w6( sxx7pmrxy-tant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 3hq ;tb,/doew hywn4nv,g3 2g 4r(0nh r7 $^{\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/ i18mi ,ichax5)saxa.+gn2 cz h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to c 5)1s xx+,anc gi8zai2am h.i75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress:d 1yfsiz01kf(p0sh a test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treh10a1k( s dsf:zy0fip admill 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 roc9pp ;fb29 ztwdk vertically upward a distance of 500 m, what was its velocity when it lefttwb9d9f2z;p p 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 wat,(tmnslr*/ig b ea 7;3wzh7gp er wheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum n, 7rw hb/7e3*gl matizp;(sgpower output?    W
(b) What is the speed of the water as it hits the wheel?    m/s