In what ways is the word “work” as used in everyday language t, 7zb pwq-:cache same as that defined in physics? In what ways is it differecc:z,wab pq7 -nt? Give examples of both.

Can a centripetal force ever do ;dr39d; fic:l lw) .ue5hjn8sum.gnr work on an object? Explain.

Can the normal force on an object ever do work? Explain in-i,,k56d 6m tsqnyv*)ixsq.

A woman swimming upstream is not movi,vxmy -2gyv6oc6*-*ij l )mjjd5 hxveng with respect to the shore. Is she doing any work? If she stops swimming a j2vmjghlvivc-5dy*6xxy6o),*m j- e nd merely floats, is work done on her?

Is the work done by kinetic fricm:dqkfa hyzi:h uxd4m: ig;; ve 9h74)tion forces always negative? [Hint: Consider what happens to the dishes when yi:a 4 :h:m;9div;zgkhu 7m4eyqh xfd)ou pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are djlqp . s;;tp.ioing no ..q;pp; ilstjwork?

You have two springs that are identical except that sph(zz) 4 dfup mm(12khwring l is stiffer than sprin1 dzhzf m2 puhw4m()k(g 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 fo-zbk 7o: l,mkdrce on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, andlm,b7o:k- dz k 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 gravi2ety mlyi xf b(0zfk/i3lu4af/ (.6tu tational potential energy change when you jump as high 0flyet 46i mx/tyl(.u/ izf3 2bukf a(as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buil9es)x 4yhl(i0 qd g1qz.ekc2 cding, all with the same speed but with different launch angles. Which one has the highest e.4 eqd cg hk9(qxs10yci)z2l speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a heightv7 og4czs 1svek6s b05 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 velzs v 7g6ob0c54essvk 1ocity 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 resrv imz;7c kpsa6c bj5x+/j*;jts upright on a table. If you compress the spring by pressing down with your hand and then release it, can the spri6kmj;*+axrc;js z p bci7j v/5ng 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,at0pctzdfhcx*w ev i+ :g6n8hp4x,4 instructor pul g,wi8p c fen*6vhxh a:4d+0zptxt,4c ls the ball back and stands against 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 gravitationgblg8vvt1loxkp76 1,he7z2 d al potential energy when water at the top of a waterfall falls tegb1l z x2kho1p67 7lg ,td8vvo the pool below?

Describe the energy transformations when a child hopashsb5vik zoau;:(nz +gx 7n0ky9f0 4s around on a pogo stick.

Describe the energy transformations thar omk ;w qqp7emh6,,:ag,c q,et take place when a skier starts skiing down a hill, but after a time is brought to rest by ,w7cek:, mqrq,agq hop e,m;6striking a snowdrift.

A child on a sled (total mass m) startifnb )hv 9y wbq-1u;d)s from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is nvhub1-w ibf)d) ;q9y friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather than stepio/a d0c: 4vympm4yc / :ovia0ding on top and jumping down on the other side. Explain.

Two identical arrows, one with ,uolqhj)d,0v e u(-f8jpb b c.twice the speed 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 far .) , dqv8feocu-0,pjbjhblu( ther than the slower arrow? Explain.

Analyze the motion of a simple swi/, rosq60mlry nging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfat6qry0/s ml,orher clock has to be wound up.

When a “superball” is dropped, cj) :l au,xem2van it rebound to a height greater than its origixa,v leum:j )2nal height? Explain.

Suppose you lift a suitcase from the fqlw9-l yv9zabk7 y81 dxhjaet4o0vfyfq .6;( loor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it keo 9-hyq9tz.qvv ayl 6; yw17jffbx48 (ald0straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather thart2u vmfnp i)ea .ya/r)nq:wq4d f/ 89n the work.

Why is it easier to climbo)og c ras,s;cac0t6; a mountain via a zigzag trail than to climb straight up?; cst go 6)ca;,rosca0

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes tofqv ;cubv*z 3- decrease 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 thizq- buvv ;cf3*s, using energy concepts.

  How much work is done by the gravitational force when a 265-kzhrr ++jz/3 ngg pile driver falls 2.80zrh + rn+g/3zj m?    J

  A 65.0-kg firefighter climbs 36lxi sf1 8n. agrjo)fa flight of stairs 20.0 m high. How much work is required6xrfn8 osl1ijfa.3g) ?    J

  A 1300-N crate rests on the floor. How much work is rodc;ium vu./jb4a 8e1 equired to move it at constant spe ojamu.b; 4d/c8ev 1uied (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 (horizon(j68ei0f 9tpdo ige8ctally) pushing a 160-kg crate 10.3 m across a rough floor without aj t8pfe6deii(c09g8o cceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a forc;stmsx gi6zkl+i)m3n7+g9 y se across a floor at a rate of for 7.0 s. Find the net9yls)++i x6t;g n7zm gikss3m work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How muchmnu,z.vk0noh/p ;o2p work i;v/hnkp u ,0 .zomo2nps required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objet1f:r atp0l 9dcts we might not otherwise be able to liff. Show that the ratio of output forc9d: t0tl aprf1e, $F_{\mathrm{O}}$, 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 ande0.uy3.(svmko+b p 1m ( 6tklce* eyqa is kept from accelerating by a mvmce b u. l013m pkyo(ey6atkseq+.*(an 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 acceleration 61mgjuzr m8 v92em:ccof 0.10 g upwau1cmj:8z9 2e c6mmrvg rd.    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 tvl vqt:x8uz319y : m2n jei5mshe distance axis 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 Fig. 6–37. 0i(aa1.bgo- r1q ku.hbtw8gqDetermine the work quqw-t1.ro aa bbg .k1gh0(i8done 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 on a particle acts ii,1o1mwzztt qe 8in14n 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, witqse cd6h-b*v6h 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 h, tgcq r85 d9*a,hc0bwmlj+dq r3t)uqas its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requircj3(+ybsrb 7r/z,u7xx pc2os ..dlwq ed to stop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250 *k2wu.osdvf8-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 ofc a4ngzauio+1z83.h u 110 N o+. iu8ch4ou g3azna z1n the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) trav.u2i )m ii, lvbhab+h 7v*foj8eling 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 iu2of8+ihvl *a,7j.)bvh mbi glove?    N

If the speed of a car is increashqho2 v9*f sn7nuz1 2ted by 50%, by what factor will its minimum braking distance be increased,vf1o t 2 nqsnzh9h2*u7 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 skid mark tosuzo7.l pzp8 fi- ms869slm3x be 88 m long. The accident occurred on a rainy day, andz8si pz ml67pms-983ul xfs.o the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By .9ma p k0ur qhiw.t a 9sv.):9,zv0es5wx jnmhthe time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air rehw x h9mz. 0.50spnamw,iv:.rvk)9j as qtu9esistance 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 stkk11b+fi9ca8jnk ypan lp oi(dtea7))s (; 9zraight up by someone who does 80.0 J of work on it? Neglect air resistance.n))e i(plac kydpz+1nbs1jkf 9o7a(ki;9 8at    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by (ff9(tb -t d7gcxjr3dl dfb*h9:wjg8 a single cable. 39-b 7*hd(fcdtgj(rfgtbf:jxw 9 dl 8 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 H)q-9n iq wbr,jxl+m;yow much must this spring be stretched to store 25 J of potential energy? )r9,qib j l y+qx-n;mw    m

  A 7.0-kg monkey swings f bg zy wa9t88ld8srq57rom one branch to another 1.2 m higher. What is the change in potential energrs 9 7b 8gqt5w8az8dyly?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter 6gr wdfbl (k99/7exhua6drp( change if his center of mass rises about 4.0 m during the ul6d r7kp6x (/w99(hge arbfdjump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kmcgf:1plp 0n2e /h when it strikes a horizontal coiled spring and is brought n el 1:pf0cp2gto 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 2.10-kg book from the g3k8k27 pa4-l,1d b6bph1 lrwwolpzemround so it is 2.20 m above the ground. What is the potential eb 1o elalp1wp3m-d28 ,p6kl4b7 whkrznergy 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 1600 m and climbs to the top of a 3300-p7h z7x/f q0lawq.;9saz:wbmm peakwa xz7z0;b7as9f:l . mwh/pqq.
(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 end of the sprig2 z i-;nx17teq0isab ng 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 -ngtb1xa s27eqii; z0 the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is ro1 o42glrz3fwcsq 3 8munning at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swin3 qcsf g2l mr83zwo14og upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from restk55 qn4*u a,dmz/vyma1uzk)o , 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 ;oz ;rgnh 19sya 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 transformetg9q ru9o5,rke za9 g1d into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 9zu51qokrr , tgg9 ae9m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a plat8v; ; -ohgk1o4abbab p+1hbhvform with a speed of 5.0 mobb; 4bkhp- g1hb18 hva ;ov+a/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 ma:oig d y:mwc9/ss), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when rele:/wm o9:cgyid ased?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides withou jiji+ t,tz.)ot friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radiusozj+ji,. t)i t is r), from what minimum height h must it be released?    r

A block of mass m is attached ep39gt lm,1 2vwb wu8fto the end of a spring (spring stiffness constant k), Fig. 6–40.,lv p81fmuwbewg3 9 t2 The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from(- lavho oeq,e1u:u1t *nnz 1q a bridge. She is tied to a bungee cord whose unstretched lengt*enz(uh 1:nve ao ltq- qo11,uh is 12 m, and falls a total of 31 m. (a) Calculate the 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 point 1 )bs a4e4 s2nr1 ,ewqf.d o1xfmwhere it is released from rest. Assuming no friction, calcufswqdoaesn xe. 4)2, 1m41 frblate 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 at an angle oft x0.r)e -s:f x1uw:mw4whmjj 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 sprilg0u1i b;m cp,ng to be 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 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 el bc;,mlu01igp evator and passengers.

  A cyclist intends to cy/w1+o tpl2qlb 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 in opposite directdif3auvx2zw+zid302/+vwd iz2l s: zions, collide headdd:+zw iwi2z 0z + zaldx22fvus3v3/i-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the+gxnxgq:i, )6ky n+l: o xvh3o bottom with a speed of 2.2m/s How much thermal eonq6+yknxl,+) x g: h ixv3g:onergy due to friction was generated in this process?    J

  A ski starts from rest and sli foco.kiw i10+des down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the ground. rd+p9aex)ue2c h4 5hb
(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 ov / wyocq3d;)1c xs3ta height of 1.5 m.cd3c1yto) s;3vxw o q/
(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 constantc ib)fzo,n4)p horizontal force of 350 N. For the first 15 m the floor is frictio))ic n4opzb f,nless, 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 coastejnpr9s*3w y afwo 91hk+v9e1q cc/v.tr in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach poin1/fotwy 3cjps+kwq v19ncar9e*. vh9 t 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches t ,e *mnh.99 ze8rl2/: dle ldwmv2k3vhhyha; 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 fii +/.1jjylys 4zgnx(srmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and rele/(1jn ssly 4y.gz+ijxased, 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 lijqt(ogr-c0fe+: hjzi c ,e :d-ght horizontal spring, Fig. 6–40. The block can slide along a table where the coeffi:jco0tj:, z q(f e+-gchid-e rcient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass f:b;8ss9ny vcj oi7ht(kjy ):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)ityk(; nbh :fsvo8j97cj:s y) 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 mf1ny2 k+x n5;eby b-jzotor to lift a 315-kg piano to a sixth-story window 16.0 m above?2jnzk-yexb 5+f1bny;    s

  If a car generates 18 hp when traveling at a steady 88km/h what must b9q:gyzcpjecd0l m(+3 e the average force exerted on the car dug0q 3: c(9mlze cp+djye to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to xs- 1xihg,odju ;l08cxr urq 8g08bd9 95km/h in 7.4 s. What is the average power delivered by the engine0i-dxqxs8lgg8,; ruu jb89 dr 1 hc0ox?$\approx$    hp

  (a) Show that one Britishc vnjv/a 2ni56 6tlb2f horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy unitsn9ai4 d r4ojl, 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 slows do +7cc(vv)c. ranfga p9wn from to 65km/h in about 6.0 s on the leven a. car)(c7vvpg fc9+l when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in+ k+vnos 7ff7a 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 takesq3): pawt)b pwkb* s7rg2 f:js 1:b:b t2rajfsw )spgpw*73) q k.5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What 2pwyltwb 69 6ra.:gw aoutput r2wb.a6arp6w wl9 :gtyating (watts) should the pump motor have?    W

  During a workout, the football players at State U23 ju+fn2 6.ff win*s6iva(bzh* (wnp :b ezbs. ran up the stadium stairs in 66 s.p+ b.s n 6*we (biz2*jun6:hns fv23fw(fbza i The stairs are 140 m long 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 cyclist))dj:,f6-3m +d z dwwqkmagh u 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 js i jgu2q+,f3 v p2n)t/kpin5steep a hill can it climb at a constant speed of 75km/h if the frictional forces a un3qjt,sp/j)vk i2 +finp2 g5dd up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg box a86r; ieopr /psm5)sbd long a level f8mis /rr6d;peop )5sb loor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.04en 0ifjl;s,5*s nhc hm.2xuk $^{\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 qs8sao( 6:ahn cars have built “5mi/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 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 b : 8os(nasq6hae, 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 fir v5bqk5.ie/nm ;ai fh.)w bfk)st shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21wv5n .i mbibh 5k;)qkae) f/f. 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 jump (Fig. 6–42) in the 1936 Olympics sho84kfux7 ot:rj ws 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 k8f4u jr7 tx:olaunch 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 looped track shown in + qemxvpz ,q4+Fig. 6–39 is tozqv+pex q+m,4 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 hizayf6 o t.kxm4e w;9q9s parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’sf4mwk9.a6tzq9o exy; 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 wd1 myl7y qbq.6tip 9t ess)69mhose other end is fixed (Fi9.t676t9mqsi qe)s1 b my ldpyg. 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 thwf6 1(2c ii)vl8bbmxcp:rny- e top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calv6bw(2 8-fyi)l cp cnrb: mxi1culate
(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 elevato -291 zikqqy.p uu3xhxb-v k;dr is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims thb, ez+ f-g.vgsat its lifts can move 47,000 people per hour. If the average lift carries people about +gb -efs,zvg.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 8s,y: 3v,xrj9wqr nif n8d6t3ea 9:,izisys/ y1 m before striking the turbine blades. Calculatsrzrn 83yt, s6:/iaw,y9qs:xifj,9 ni 3y edve
(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 veubudsym g y53 11j; 9poic7(hnrtical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as youriy 7sgu53djb1 pu c mnoy1;h(9 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 convevgs tw0b 91tehvh4 -3ert a candy bar directly into work, how high could beg9 w0vt34-h1h es vtan 82-kg man 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 upward ann9c.v6 ha:-hv: v2v7d aicfjggle 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 inside the st*incne i9n:w9ejimq/h2l 3drx;;v.cale compresses 0.60 mm, and 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 pea:jlm 3w h/eixqviie 99t;n cn;*n2. drk?    N

  A 65-kg student runs at 5m/s grabs a rop+rf)la9 xurn * h+.eztt l6 ssp2o1d2jx(*q lee, and swings out over a lake (Fig. 6–45). He releases the rope when his velox+16 9o*f( lzt rlhetrus+slnqjp * 2ea2)xd.city is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m ill- tueon ,dzy .5, 3vd,vumb7n 9.0 s. What minimum power output was used to accomplish this feat? 7ve ,bz, dt .ov ,lmy3u-dlnu5   W

  Some electric-power companies use water to store ene2tuxb)i *jq 6j clix4ksjy99:rgy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0k i u*9qi9)tjx:ly s 6b24cjjx 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 thrlpuag-khic g6y2b6q s47wg 2 vg9-,we spring stiffness constant cakgh isglbr 2 wp7yg266g-vq94-uw,for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m jadu2(-pj2dyz6/.n2b ddcxa 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 fro p0u: lhe4tmu0m 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and nlh:pu 0e tu0m4eglect frictional losses.    s

  In a common test for cardiac function (the “stress tuaki* 5.nm:im est”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-*muamn5. i :kikg 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 500-kg rock vertically upward a distance ofo 0k:pu*yjhy/ 500 m, what was its velocity when it left the volcan hk0/ujo yp*:yo? $\approx$    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 w9):fv-qyq -hja0w zli4m( zcfrom 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 if-z9a04qiy:)m qvz(jw h-l wcs its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s