In what ways is the word “work” as used in everyday language the sam9hp6 8vk3q fshbu1mc;e as that defined in physics? In what ways is it dibh;s cfm3u 6q1hv8pk9fferent? Give examples of both.

Can a centripetal force ever do work on an njjo5*m: ttu oa;58peobject? Explain.

Can the normal force on an q,iw/88 prcmukrz3t. object ever do work? Explain.

A woman swimming upstream is not mooj3c+*t* jc y:) lpepmving with respect to the shore. Is she doing any work? If she stops swimminmtpj*el+:3 ypocc)*j g and merely floats, is work done on her?

Is the work done by kinetic friction force hv.kms4+ ;otp, m y)7qeua.jes always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out fro4ahs.tqv mm yo;7k+.e,)u jepm under them.]

Why is it tiring to push hard against a solid wall even though you onfkbz /g- *c/are doing no w/nb -/ o*czgfkork?

You have two springs that are identical except that spring l isxs/f/1(whejy 87ya r s stiffer than spring 2 xaj/ 7sf ysh ey18(r/w$(k_1>k_2).$ 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 forcgccw/ qs 147fyci-3uddfp*c( 8s n4fl e on a block that is free to slide on a frictionless surface (Fig.6-30). The bloc3 s wnd (fc7sl 4c/g8 iqpc1ufy4*-cfdk starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change wa6 y +;t1 ox1ihf +aogog9ce7zhen you jum+g zi1foo+9aa oygc7; 1ehxt6p as high as you can?

In Fig. 6–31, water balloons astcb.ho0w *nq.zi)kwb h8;v0 re tossed from the roof of a building, all with the same speed but with different launch angles. Which one has tczh.bw8siokv .*0 )qhbnw ; 0the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point t 645afaexhke ,hat is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On theh a6ea,5efkx 4 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 table. If you compr-wvl(v8.uq7svr ow3qz6 e y4 ress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the la83 vvroe.r v-z64q qwyw7u(lsw of conservation of energy.

A bowling ball is hung from+gecd(9wp:+nrn fxj d cj(n09 the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball agains jn +cenxw( p+dgfj:( 9r9cnd0t his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy we qhzk3 gy./23l5f:+2vl cjxg5 3b rpkcbmsz6hen water at the top of a watergyhcvxlpqzc.erb5jb 5 6zm/l32kf+ 3 2g k: s3fall falls to the pool below?

Describe the energy transformations when a oz2g5lz+. st fchild hops around on a pogo stick.

Describe the energy trajd38 b)souu1pnsformations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking 8bu)1 psj3dou a snowdrift.

A child on a sled (total mass m) sho ht7hy:8q-ttarts 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 friction (deep sno qt h7ho:8h-tyw)?

Seasoned hikers prefer to step over a fo:9r oi e4o7 d.9 gnjvx)um8nzallen log in their path rather than stepping on top and jumping down on the other sideo .94d nn) e8 ogr9m7ujivoxz:. Explain.

Two identical arrows, one with twice the speed of the other, are fired into a bow (uy;v, t tkny(1,khale of hay. Assuming the hay exerts a constant frictional force on the arrows, the (w y;kv,otk, (1thyun faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum i;gw2rfa d7f-s/j iv*v n terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grand j vffaid7*2v-;gr/w sfather clock has to be wound up.

When a “superball” is dropped, caea0c4a (7x* ndqd-lp kn it rebound to a height greater than its original heigh (a pxnqd0ac*l-4d e7kt? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on t8fe+e -.d8ak l fkpl+nhe suitcase depends on which of the following: (a) whether you lift it straight ukd ef +8.-kla8pnlfe+ p 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 7f)l* *oupc itneeded rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb strg5 yo0dqd 0z8qaight uy0qddog 0q58z p?

Recall from Chapter 4, Example 4–14, that you0- sr3 qce15oz5be swc can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy ecscbqr031z we s5 5-oconcepts.

  How much work is done by -f/c0)x cw cr8eup j*wthe gravitational force when a 265-kg pile driver falls 2.88) cpx0w*-cjwc /reu f0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How m iw*nhav3zr7s(3 e8mnuch work is required? srm z7(n*3vwe3hi 8na    J

  A 1300-N crate rests on the floor. How much v*u;t+iih0 bb(uslx c sypsr /s .dib 21k1a3+work is required to move it at constant spees;0v1 cp ibxku1+is+yb3t *d2is (srba/uh .ld (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 qsdqyyo j pc2u *d9d 1()3q7dodo (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without accelerat2yd7(o3q qcj upd)dsd1 qo* y9ion, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor86ty5,cb6smn ;btbrf 8 fquv + at a rate of for 7.88t, fb nb5tvycf 6umr+q6bs ;0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How mu,+-b 8rpqmxqjch work is required to stack them one on top of another?-8 qqm prjb,+x    J

A lever such as that shown in Fio4s krk,(ux y)g. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output s)4uy (,kkorx 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° in3 *:sxa4c *s uxje642yfivjxkcline and is kept from accelerating by a man who is pushing back on it parallel to 6 *cy2vefxsaxj: *xu4ik3js4 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 gi.ry1fvgpr(,k 5k// 0pdyrxf pve a helicopter of mass M an acceleration of 0.10 g rpxrkf.p,r1y yvk5 g/ ( pd0f/upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is linear -huw o 3h /c8ptnw/o *e8c6opxand 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 axb1zvq k- zg6 s+6z rpzfn51me8is, varies as shown in Fig. 6–37. Determine the work done5z81 z mkszf1nzv6 pb-+q6ger 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 par mc(.t,5gaid pkk;(t. misd z*ticle 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, witdi) v/a gus-q gr;ikq95(a5n8 drv- lwh 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 jk x 0 wza,/mo1 .v98uc*fecrmits speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requg e8 mw/vsomg.i* (sqo3zm- 6nired 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-kgcar travelin;+sda/de 2 q b1gwc.gig at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from 2(z huej/0 uzxv/mb,qa bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is theh/q,2 /ub0je vuxzm(z speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward qgr t* .rq7-a)ser-md25 cm when the ball is caught. What was the average f)g .*qea-mr rr7qt sd-orce exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its mini 47m cmi - x+tyrr0uq ab.os3rtsi;t:9mum braking distance be increased, assuming all else is the same? Ignore the drti;s y7rr riux94 cmt-03baqt:m.s+o iver’s reaction time.

  At an accident scene on a level roavv7e ;l* njvf)d, investigators measure 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 ( ;*lfvjvn)7v eand locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a ma8juu :.tozofu1*x2uhda)a0n6 c. foi n*g; twss of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance nt*ozxa)0 ; 1f8gjucu:. if ta u2nw.hou*6odbetween the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight*at. qa ectbt7bb .j;- up by someone who does 80.0 J of work on it? Neglect air resistana*b;cb7. at t-t qbej.ce.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a s *xb2ubq fxr.6ingle cable. xxq 6.r fbb2*uDetermine
(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, ) x*gand(*j9rx y ,dqjof 440N/m How much must this spring be stretched to store 25 J or(, n dx9*jxy a)qg*djf potential energy?    m

  A 7.0-kg monkey swings *lb w ;2nfk; uv+2jvahfrom one branch to another 1.2 m higher. What is the change in potential energ+wuf hj;v22bl*;an v ky?    J

  By how much does the gravitationalpijmxf1,h()l th k7 9fx/pb3m potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during(t3 ph b1,9k h/ plimx7fmxjf) the jump?    J

  A 1200-kg car rolling uxd h d(hy+;q3tv-h*z on a horizontal 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 constant ovdqxt yu(+h3h*d ; -hzf the spring?    N/m

  A 1.60-m tall person lifts a 2.10 .vwkwjj e0s0,-kg book from the ground so it is 2.20 m above the ground. What is the esk wv,j.j0w 0potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the topp-pm.g ovg1wf3bv/5/f(wpyv ;yvy i; of a 3300-m peak. gw v fbv.- /( 13/ywopifpvmy5p;gv;y
(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.uc r i0ji-6azv (:cakkv)pn/6 The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, whuaj6pkvcz-i )k0/6 (r:avc niere will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running atyqi1.vlaq g( 976losqyn h46g top speed (5.3m/s) and grabs a vine hanginglgaiy6n (l61 9s4 oqqqh.7gy v vertically from 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 frictsg p71n z)2osy*ds/pg+jfos:ionless 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 uzkgz* dl4 )k,op 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 transfokrpzsvb8-r*c 1) x jmzv 6ws7kf,.:harmed 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 orw-jc8 ba,kv*sp6f1zksv:r z )hmx.7f 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 from the top oglp, y45ipi 8(s,zj jpf a platform with a speed of 5.0 m/s. ,s,yijp l 8p4zjpg(5i($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignore its mass), whose spring stiffness constx6 j;;imepp mf dt:++iant is 950N/m is attached ti;:+tmpi m+ed6jp;x f o a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction ale0bs: aoj5 q:)7t4om v5ovvuwong 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 radius is r)4o5svo0tqv j75 e:uv)aob :mw, from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffnesss2jw8n uai sxk 3(vpj)c h;q 3uew4*i+ constant k), Fig. 6–40. The block is given an initial displacemen) 3 eu js xvkpu*j23sc +h;niw48(iaqwt $x_0$ 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 fk9. r9h-c0ayxvfzo ( from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring st 9y.(0fh- ov9xakf zcriffness 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 where it io t nhd.h)*9tus released from rest. Assuming no friction, calculate tod9h* t.utn h)he 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 anglv6:l2t 8mxeh 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 ;9mnu*ykz;tay+ nm sn -g* /wnspring 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 9s;m+y; gunwkta**n/ynz- nm elevator and passengers.

  A cyclist intends to cyclev/u l/j5e 9oq-8 wpkid 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 oppox6 bh .tlgf6ar7ka97+srykm 6site directions, collide head-a9s+7 fy 6ktk. rhl6xabmr 76gon 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 amlw-tp*4zz8y5 ru jmw4( xgv,nd reaches the bottom with a speed of 2.2m/s How much thermal el ,v4yt (wm4zwx8m5r -j ugpz*nergy due to friction was generated in this process?    J

  A ski starts from rest and slides down ake -rq p2 v*ns3n77uva 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 gy9 x/(78b0 :racn4dlvwyoy1 8uvi kn 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 height of 2.0 m, and it bounces back to a height ot06by ry5. tvcf 1.5 m. byc5 v6t .ry0t
(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 acrossf- w6mnz,w wa1 a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionlef-1nwa,z ww6 mss, 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 passes point 1 withz 6t.dza1zh(d o wm,jh4c.t9lo6 8njb a speed of If the average force of friction is equal a46z9ob6dzj ot8dz. j. cwmn h1l (th,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/s0kw wp82tzta9 3eqzr 2 reaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring (kcsd2 d09 re;nwr-:qre=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. qecs0dr-2 dnr: ; 9erwWhat is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is fij ah9(y xb-fzi.d4, kigvp37 krmly attached to a very light horizontal spring, Fig. 6–40. The block can slide along a table x- ( y4g ajzidvf97,bhk pi.k3where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg includiq-lc 9i 0evrn6 -bl1fc+ .ooddng 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 wo1vo9bo r-6nqd ce ld-0.fl+ci uld 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 pias bw co8c*l-g*no to a sixth-story window 1o*l8 cgw -sbc*6.0 m above?    s

  If a car generates 18 hp when traveling at a d0jn i9p; o8vgvt;r ,rlsrx.-steady 88km/h what must be the average force exerted on the car due to friction and air resitr9j;nl0 ;vxv,pd8 s r.g-rio stance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7w:u)j6gjkh-tti 1z . z.4 s. What is the average pthzjwu-gk ):1t 6jz.i ower delivered by the engine?$\approx$    hp

  (a) Show that one British horsee7* 7kk*pth-.ylkrq kpower$ \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 arebgeno lo3.34o 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 tha/zu rc8q2mqk 8:xc6vut her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep theuqv6k ur /:x8 z2cqmc8 car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motw0ymdpr v+t:pt uel:w3 ,;r, tor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 1gz8 (qdexj(+e f9dec+ 2wtc-k4m/s If this motion takes 1.5 s, what average pow(9 wt +f2k+xjg( -cd eec8qezder was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of jo xw4wb7e)un-d -vz33.60 m. What output rating (watts) njx dzwb4v- -3)eou7w should the pump motor have?    W

  During a workout, the football, +x1dfdhw f na+1*zum players at State U. ran up the stadium stairs in 66 s. The stairs are ,h1 fxafd+d m+1unzw*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 clcl xkki4w xj:5 f:(fgnu.j (6pimb 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 m x:zx):ffodr 76g-zsqw4mu-x-gy -f8bfw q :paximum power output of 120 hp. How steep a hill can it climb at a constant sp so)d4 frm6:wpg8f- w --u7:z fxy-qxfzb: xqgeed 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 alony1,,e8lhqrt us 1ke9khc.1 i5bp x+ dlg a level floor at a speed of 1.2m/s if the coefficient of fric,ut h+rse. 1e5b8,li 1y dx1q9lkphck tion is 0.45?    hp

  A bicyclist coasts down a 7.0zpv9b+ se*h 4v /m mgyhd)vm7: $^{\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 carsy muu7*g1s qn7fcj535jdroz 6 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 d1 jo575fcm6rusqg7u *z3 ynjbe, 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 firsta9kju zn4k9es3k ; h0w 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 21 cm, and an average shelf0hsj;n 99zea4ku3 wkk 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) n x64n*ft l.jein the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of txt .* j4neln6fhe 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 40rzvb1ic a l60ej8o9kxn,yfthe looped track shown in Fig. 6–3kje89z i cv01o6rn, xl4af yb09 is to 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 4hp, -e+v -eg 1+ ap6givgmikam after jumping from an aircraft without his parachute opening. He landed in a snowbank, crea1+h-gg+4p giv-e,p6evim a kating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fixft8 64mn6 xtzxed (Fi m6fztxxnt8 64g. 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 moj+akg-w- xm -vynn6s9 untain. The climb is made in 5.0 h starting at an elevation of 2300 m.gsjmk-+xa- n-v96ny w Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a halv0lg t/jlfijk:);h 1 g5o6juge 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 47,000 peopb h1m drp3sv2 6 wvatj()w9xs1le per hour. d231m1sahr)pw bx( 6j9tvsvw If the average lift 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 vepu: :2e2 1czfs yjt;*wt vf)xwrtically 81 m before striking the turbine blades2tf:tx1pv)ze*;fwuw y 2 cj :s. 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 circular v( j,imt1,4 ppdbow3 5xpf/y jueaet-/ ertical 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 ,ympj3, /1a/u tfw p ioje-te5xd (bp46 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 cr(h,x: axuvpio2 s9p (onvert a candy bar directly into work, how high could an 82-kg man climb a ladh:avi2( o(r xu, pp9sxder 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 firedmvff5h7+ i )kk 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, the spring inside the sc7ym/zi rp p3a6ale compresses 0.60 mm, anrpay6i7mzp /3d it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lake (Fa24lb x(kxx ixiz)3-u ig. 6–45). Hel4x ux2z3(bxii xk-a ) releases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs ;sjxho4i-bq 6y( m1icovq;l .+aoz v,a vertical distance of 5.0 m in 9.0 s. W4lv(6s;jbv cx.-,m+aohiqo o;i zqy1 hat minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store eneinu/ou pvn eh3l+ 1e82zg7 .rkrgy. Water is pumped by reversi 1pnz +k.r2e 7eig/8lu3 ohunvble 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 constant k is cut in half. What is the spring st88j6;e+ ejajxq)xxxa sxxv .1iffness constas.x xa1vq)xexjxj8 8j;6+ xaent for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up g1oku(rlp55b a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to **43h;jm dd5d a3:t lexpsouj55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75m53;d**ojetdj4px 3 alh:d sukm/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), thelx5r0;7hyd4y ( uavwu patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping at an angle ofx5la y0v74 (drwhuyu ; 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 distan0qp 0f;bn hi3 vf7hi9tce of 500 m, what was its veloci0 tfn hv7pfq9h0bii; 3ty 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 from a h pb5n x5+sqc9dd:,xikeight of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is sip5n,d +b:9kqxxdc5 its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s