In what ways is the word “work” as usyg; 7kogfos8re5u d09ed in everyday language the same as that defined in physics? In what ug oegf507s rd9y8ko ;ways is it different? Give examples of both.

Can a centripetal force ever do work on ,a1oueqxpi1 0.miu/d,jse3w 1hxzj (an object? Explain.

Can the normal force o bo(vcq9dbo/ 7n an object ever do work? Explain.

A woman swimming upstream i/8mbhofc 8xe,s not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on her?/8mhc, o xfbe8

Is the work done by kinetic friction fora5 srmof6ua 8y,jl x;:ces always negative? [Hint: Consider what happens to the :,xa;6y5fjusl rm ao8dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against uzr* mbfz5 -k45egd0 .jdyt+ga solid wall even though you are doing no r5 0-f.yzz*dm ejdg+kt u b54gwork?

You have two springs that are identical except thatgdh gumvu4+4 l*+s3rv spring l is stiffer than springvmur4 +g*4l vsud3g+h 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 fe/ d:2)z myrfa block that is free to slide on a frictionless surface (Fig.6-30). red /zfm:y2f)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 much1/novhp u 2h*senl* j0wlx5f6 does your gravitational potential energy change when you jump as higw/shx 2n*o *l nl15vuhjf e60ph as you can?

In Fig. 6–31, water balloons are tossed from the roof of a eiy -/136 bm2dlfeji vmd4j+ mbuilding, all with the same speed but with different launch angles. Which one has the highest speed on impact? i/3m4d6ifbv memeyj2lj1d +- Ignore air resistance.

A pendulum is launched from a point that is hpmfp9n6o/s) yyd9 m(a height h above its lowest point in two different ways (Fig. 6–32). During both launchn ms yfdom/(6p9p)9yhes, 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? Explain.

A coil spring of mass m rests upright on a rnj(3z.h9cb0y l+8. 7fo*fvirkpn b stable. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservatioz.r30*skf7obhf (npi+9 b8nlcr jy .vn of energy.

A bowling ball is hung from the ceiling by a steel wzj,ntm2 ,ptuk o zr k38zn2z6:ire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avku2:p83n,zmtk6o rt zn z,j z2oid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the v2/8mxxck- wdzt,1 e atop of a waterfall fa/xex8ktavm2, z wd-c1lls to the pool below?

Describe the energy transformations wh,xg*. t;uha paen a child hops around on a pogo stick.

Describe the energy transformations that take place when;xzzj l +fkxa4nbl l:cl- op/4x,le* 1 a skier starts skiing down a hill, but after a time is b 4e zj*-/xlpbl, ;: 1oz4kxl+fc xllanrought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at hdnrmclaab j. m8g3* qc8r8(: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 *8 8 a 83blg.mdrcmq(a :hrjcn(a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer t 5ame;t5, dlpluiw) rv fw5 cm-4.sbv-o step over a fallen log in their path rather than stepping on top and jumping dodb tu ai5lsc4wmfl;,vr)- wpm v55-e.wn on the other side. Explain.

Two identical arrows, one with twice the speez8d (ypv:7(xoy0-dub w nyc )od of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much fa- (y:pzu 8ovyoc( 7dyw)0nxdbrther than the slower arrow? Explain.

Analyze the motion of a simple swingin;8)i ogosgeb1390es1pwmu qy g pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why 8uoebmi3q;s 1s)w gg 1pey9o0 a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater/ r3; gzfukhyxup x8 /vhc088r than its original height? Exp/fxku8ruy vh08z;g83cxh p/rlain.

Suppose you lift a suitcase from the floo1 i5p1l 3yjuymr to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and3u11iy 5 pjylm (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than the wor- -ur/fl;y(e8wx wor5 a, wpojk.

Why is it easier to climb a mountain via a cr pvv05bp49 azigzag trail than to climb straight upvab5p4p9c r v0?

Recall from Chapter 4, Example 4–14, that you can use a puf gojh:wgh/+l)r+z8 nm v)8 ce o.q0iulley and ropes to decreasefgwho j /) mrei hoqz)+880 +v.g:cunl the force needed to raise a heavy load (see Fig. 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 a 265-kg pile driver fu *muas n*s)ug,qtb 2tu(t7:kalls 2.80 m2* tusqubksut ,)m u7g: *tna(?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m h5jnk0,h,tabtrn5t ei9v k *l.igh. How much work is required? *thkvblrjkn,t9 i 0 te.an5 5,   J

  A 1300-N crate rests on the floorn4iv4llp +rk u8 3xy1c. How much work is required to move it at constant speed (a) 4.0 nryu 4xpll8ik cv+413m 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- xsc7xuv1xd6-d4 w s)c 1uy4plkg crate 10.3 m across a rough flwsp 1)c7dxy xu6uxl4dc 14s-voor without acceleration, 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 x;*5 ) ;fx8+gonytc km-x1uqvun-cssa rate of for 7.0 s. Find the net work done on the ck;g vxo)c *qufsxt8; xusny -+-m51nbox.   J

  Eight books, each 4.3 cm thick withup6,-/ dqsmr ilrg1g3 mass 1.7 kg, lie flat on a table. How much work is required to stack them one ,6lrpqs/-ugdrg1mi3 on top of another?    J

A lever such as that shown in Fig j4dn3v4f:itk)5o xaq0 cn+cj. 6-35 can be used to liff objects we might not otherwise be able to liff.vc5jxo4ntc 4) :dqfinj3 k+ 0a 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 isv-ou ray1vd*u, 8v db3 kept from accelerating by a manvrd u* 3ov ad1ybvu,8- who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an accele+1 j 1 fepmv9g+ihbkf.ration of 0.10 g upward.pij bkh. v+9f+g 11efm    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 c le+l t)k7tl8axis 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 x43kq,og ium;b axis, varies as shown in Fig. 6–37. Determine the wokbg,om 4q iu3;rk done by this force 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 csh; -73*smpq d wbos+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 oxygb3*5 og;znji hjtt);/i*obgsx : r w.ken molecule, 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 its speed incre*8cemk5p;7m so cwdn/adh ;v0ased? $ \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 8bs5eav :a yzv:xad *5azbv4:$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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-k dqtv. q+y;yeo92n qc;gcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired fro w/hmd. kropir8r45r v,vt 2*mm a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arro,hv4*v 8i.2kmtr r5rm/wprod w as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fiele cg/- q c5o(83en ttyg2lm)ohder’s glove backward 25 cm when the ball is caught. What was the average force exerted ) t congogly8 mq3ce5/(et -h2by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum brakiw ic:6ky z;n:rng di :ycwrzi; n6:kstance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s cy7b-e404w/t x:lg y ;po j/qj-qzmu pskid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be :p/g-yqj/we4uo z7ltyp j4 m;qc-xb0 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 :umn/rh0e 7pb at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average forcee7rnph0ub /m: 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 by someoj uqyysx p, q 2u;*auo33e31r7us :qyxx .n6qxne who does 80.0 J of work on it?ys. uuqqx,3n: e ;6xq2qu u xs r*pya73jy1ox3 Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accele zfu f6z/,lsa *,hrq.b g//xvhration by a single cable. Determf* r/ /x, hugb.sqfh, l/zzv6aine
(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 stif +2 c/jz* s1voq4jwxqsfness constant, k, of 440N/m How much must this spring be stretched to 1 oxjqzqscj 4+wsv/* 2store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Wh2.stqlg*/tbj8bdrp 60 v wr 7aat is the change in pbrps d8q2w0rtv t *b/6l.gj7 aotential energy?    J

  By how much does the gravitaptxu c9ct8ehdqgit 2wtmpfc--lg,/7- 9+ +ca tional potential energy of a 64-kg pole vaulter change if his centtt-c pcc/+gti felq8adwh , gpct729 -+9u x-mer of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a hor7t( ur+jpvpvq* z:-g vizontal surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constq:v-ru7p+pjvvtg* (zant of the spring?    N/m

  A 1.60-m tall person li7jf*bo)2mr(8qf an qofts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential eo* 8q2b (fqa7)o rnfmjnergy 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 elevation of 160wlyuldvu4y- wcjbjd 92 d5*1( 0 m and climbs to the top of a 3300-m peak. 5*u4wyvwl(-udc1ydjljd29 b
(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 h7o/:t;5k(b5vv ovgq t bx;e lgangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on bv;bvet o k vqg 5;o(t/xg75l: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 spb ve: zl; v. :t,gakiigi3yz(: kwx;x2eed (5.3m/s) and grabs a vine hanging vertically froivw,z:ibgayxki: (; 3l xtkg.z:v;2 em a 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, starting from rest, slides down a fric yvzox;,)ga dz*8nl9 ctionless 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 shovy 5ij6, /. (si 4hhnd9npahu+qzing6ee up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravitat.p*xo zab8o/q fg: mj)jt,hbg4c p,+ hional potential energy without the aid of a pole. With what minimum speed must Fran 4 japmbgxgj.qz8hp+, /ct: *fbo o),h 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/7n:nc 0ih,mb+3npn3 z z cbnrm the top of a platform with a speed of 50r:ni+cn ,hbnc7n/bzmpz3 3 n.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 its mass)cs.gma i 5cj+wd2 l )l:fea2y8, whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed c2cl f2aim5sl)da wy+ j c8:e.gan 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 igl g 2be:)52yr6uacd.;rwt athe looped track shown in 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 heie6)alw 2dyg2iburrg:. 5; atc ght h must it be released?    r

A block of mass m is attach33jca-;wwahe7oqzao,y)/ eyed to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displaceme)aqao/,w-j3ewhzo e;yya7 3cnt $x_0$ 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. Shev y)30,wi fzdd+ d 7c)dj qtrmoj,-3bb is tied to 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, assuming , 3q,od di7b b dj0 wyt+f)dv)zjc-3rmHooke’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 poia b.do (v7,nuhnt 1 where it is released from rest. Assuming obu n.ah,dv (7no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s 4bl 2ajw )fbvh1(tlt6j o76hcat 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 deskgqn**) 3z spring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevatg3ekn*dzq*s ) or is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle ur wes /- hef)3-s+vpvx9q,a ftp 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 mazj h s9w40bzo3ss 7650 kg and traveling 95km/h in opposite directions, colli 9hz3bzsw 4oj0de 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 th-5v0rap wuz02bhm2xto)-88p ai acqhe bottom with a speed of 2.2m/s How much thermal energy due to friction was-8a8ob a0ar h5u2p-wzpcq m0tx2)ihv generated in this process?    J

  A ski starts from rest d,1 b mxdg 2igr7pqy9)and slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above thfuzppq zi52u64d 22cze 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 heis5cesnrogv6.)w4ng7opn n(0ght of 2.0 m, and it bounces back to a height of 1.5 m.n657(wo)gvnn 4eg c0s. pnros
(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 0y u.prmc 7n7g 9nayzx(58gtgrest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionlegnx5y yt0rp9.(cu a8gz7ng m7ss, and for the next 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 pa,y)mcmlaaufpdub w-3k/0s4 (sses point 1 with a speed of If the average force oas 0-)m/kl4uufp 3bac,d my w(f friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of h/f ;bd0w qrx5y)bcx 9a 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 horizontojfb*gt*xla- ;eh2 l (al 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 oj x;-e2blgo( *th laf*ut 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 horizontal spring, Fig/t)dgsdpb0f: . 6–g/ f b)st0dp:d40. 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 swing?    m

  Early test flights for the 86i, ht3v)( bduyisymspace shuttle 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) What would ii36t(,m s vbhydu 8)yits 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- r, +im6sr7pe t:sdi67ll 1kvakg piano to a sixth-story window 16.0 :+e6rdkir,mi1a l 6s7s7tl pv m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the a;pzxfxj/:: ch- +rbunverage force exerted on the car due to fric:x u n-cj/h+bpx:r;zf tion and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 bak38 j9 35ehcabcsx5s. What is the average power delivered by 3ab he59bjcs kx3 a5c8the engine?$\approx$    hp

  (a) Show that one British horsj7/8 5-epj nlp uxj7rqepower$ \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 “b43fr gea5 tcp2j1*btkilowatt-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 to 65kf8 -7arx oj,tlk /3becm/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keepfb378o- c,ljxkr /eta the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 hx oad ui,l w56 j20e5 8)zvkvn9me:kox? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a j5ir kyz)e:r5 7.3-kg shot from rest to 14m/s If this motion takes rz:55ijke )y r1.5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through nd0+lbpr n gc;-.ump3a height of 3.60 m. What ogdnm;ru.p c np-0lb3+utput rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stom38 mhvbes- y1n 05yc ax32fzadium stairs in 66 s. The stairs are 140 m long and inclined at an ang0 3c3m2hoxyase85y 1v-fnb z mle 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 clim;t ltle/ )*zyub 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 a hill can it cp aj5 sw6eu8x2limb at a constantj6 8uwx5ap e2s speed of 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 310-kg box aloh0;ub8p;n(l pdgv -j3 w rgxn,ng a level floor at a speed of 1.2m/s ifg(v;0-plwb ud3np,n8;hgjxr the coefficient of friction is 0.45?    hp

  A bicyclist coasts do;sihh ois7+u)mdcj 3-d6y2 pywn 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 “5mi/h(8km/h) bumpers” that are d,hfb(nzc)vd2* rf w*wesigned to compress andfw) hrz d( vwcb*,fn2* 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 the ground, and the remaininknnzr vt8svj 7( *1-s t.jmtk3g four shelves are each spaced 30.0 cm abot8nv1znv m-.skk7j ( *rt3sj tve the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jaj+-m ,plrm g(4d an6iump (Fig. 6–42) in the 1936 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 was travrmi4-+nd mpa 6j,alg (eling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along q /-y3.fp7q m1x- ds7vfj evbythe looped track shown in Fig. 6–39 is to remain on the track at am/ pqes y.q7x- jv1-fb73yfdvll 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 afe4 6tpgfhzh;5jxd03 xter jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminalgj;tp xhh430 ex6z f5d 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 other end i1f.y r2 wez;n;w*e ms/k9zeqxs fixed (Figrx;qm. w k;z2yf1 nzw*ee9s/ e. 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 3700-m-high mountain. The climye+ f.s/ josw49 jeh5eb is made in 5.0 h starting at an elevation of 2300 m. Calculate9wfs .4yh jjese/ +5oe
(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 aecgt pfpk* :tuqjtrm 0-8(:oharrj ol-*)*(p bove 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 that84q agi;fxy jqdu-bp g1.z-; m its lifts can move 47,000 people per hour. If the average lii. ga;m-d4ypuqj-81 x;fbzgqft carries people about 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 beforevn-w/pn9r3 h( 9lbt yc striking the turbinbt( r 9/vylcwnp3n-9he blades. Calculate
(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 circ8h -25 qogxv/1trtj8kpansv o0*adz-ular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop atr a *v/jtdpa v5xo8-- hso021qzn8kgnd 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 candy bar directly into work, how high c iq0v nb.r)610zr,g: uffe hsoould an 82-kg man climb a ladder if he were fueled by one baro 1u.s,06qrnfr bhg fv0ie)z : (=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 firemv+v bfb //,7aaya:a x sig58kd at an upward 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, th fw1*xz5ic0dpo c2 bs*e spring inside the scale compresses 0.60 mm, and it tells you yodo02z1 *bws5xc c ipf*ur 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, and swings out 4 ;w-yq7cc41sy )6u hcthypjx over a lake (Fig. 6–45). He releases the rope when his velocity isc ;q6h)wtyhyp u4jc41 yc7- sx 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 *st 7zgab .gw;lbi:r48 6 lkybvertical distance of 5.0 m in 9.0 s. What minimum power output was used to ac.k:gr8 b*bsbw4lt gz;y 7lai6 complish this feat?    W

  Some electric-power companies use water to dv:g5 oxdjr6:store energy. Water is pumped by reversibldo:xdg6 j:v5re 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 cons0f(86/ya0x rv tdi, 0w3/fffbg* m* pfvmnvmwtant k is cut in half. What is the spring stiffness constant for each of the two re wi0*tnbf v,m/03frvv086/pf* fxy(gafmdm wsulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a 0 : pzi): uyfwfp:w/ydt+:qb yrough 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(evm9*cvnds dsh s(4 * from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h m*sd (cde( *9sn4vvsh Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient5g ibam8 c;d88yn/dqy walks on an incliney/ q8 ;m5y8ddbgin8c ad treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient 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 spews a +2xc3, ynfsu s500-kg rock vertically upward a distance of 500 m, what was nys, u2c+ sf3xits 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 wheel flatawa s).buujs/, 0 0rom 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 iub,asalswuja.00t )/ ts maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s