In what ways is the word “work” as used in evu022xx; qzhd ueryday language the same as that defined in physics? In what ways is it different? Give exauqzx2d; hx2 0umples of both.

Can a centripetal force ever do work on an object? Explain(uz3 7tqdkv6m jsj(s/.

Can the normal force on an object ever do gseha o4asp0x;a m0-enr j30( work? Explain.

A woman swimming upstream is not moviyt)kk/h 8eoo/ng with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work done on oh/)o8et k ky/her?

Is the work done by kinetic friction forces always negative? [Hint: Consirb. 2,)uqfw pyder what happens to the dishes when you pull a tablecloth out from un,w fu2p.yqbr) der them.]

Why is it tiring to push hard against a solid wjf+3gl+(n2 b btht8elall even though you are doing no wnb28g+j(fle +l t3bhtork?

You have two springs that are identical except that spring l iss9hc(+x8wdh;9lpg r x stiffer than spring 2gph;9s cx9lrxh w8d+( $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is freeo j5t8g*zq, cr ;.vfvthco7 *e to slide on a frictionless surfa,q58jg ;rto v.ht* *z7ccveofce (Fig.6-30). 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 much does your gravitjepu-s zf+8j/ational potential energy change when you jump as z8+f-j/u jpse high as you can?

In Fig. 6–31, water balloons are tossed from the roof neslq+9nv dpxa np37c5) pm 6-4vf8n vv+lv0cof a building, all with the same speed but with different launch angles. Which one has the highvf8 pvxl9vd 70n 4+cspqn n6ape+3 cnvm-5 lv)est speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point incs:p ag8l:ancl ,*hwfcf -25h two different ways (Fighcg:s5 ll,h-fac c2n:w8 p*fa. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the spring 2v. 8 ,no9y1rwnvfathc:ini:by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of consevh 91.:ricv tif8,nyw2 oa nn:rvation of energy.

A bowling ball is hung from the ceiling by avvzka8xzdg - /03q d ys4b4t:b-tng2e steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall/e g2xgs 8d3qyt40 vdkav nb-zt :4-zb 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 gravitational potential energy whk(:k bxhp * 4bmm*+n6 3ztktwaen water at the top of a waterf ttwxkb(pm3zhn 4*k k*6b +:maall falls to the pool below?

Describe the energy transfor3q, m .zyak5qkmations when a child hops around on a pogo stick.

Describe the energy transformations that take place when a ski rbh*r4 lw,m4;sgfd5 ger starts skiing down a hill, but after a 4l*hdg bs;r 5rfgm, 4wtime is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hill of her xizra)8u06x *h h*ltight h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it iaxt0 lz 8r*urh6)xi*hs icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to stzkt aet2;1z06pzfrq .ep over a fallen log in their path rather than stepping on top and jumping dowp z r0e .6tzk;1zta2qfn on the other side. Explain.

Two identical arrows, one with twice the speed of wk4 u*w*id y,iha3x 8cthe other, are fired into a bale of hay. Assumi u3ixw**4 hck ywa,i8dng the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a si8un+zr55wjke6 fcqs. mple swinging pendulum in terms of energy, (a) ignoring friction, 6kw j8.nes+fz5r5uqcand (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it re +gg1o .hbt f12hnuzm8uz2f1 q lhxt +308ycfjbound to a height greater than its original height?. f ybzz8xf1mt2hh2gulquc1f0 1n h++ojgt38 Explain.

Suppose you lift a suitcase from the floor to *b rb xaqcf,53ad2,e ba 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, and (d) thb,a aq ceb *2bd5frx3,e weight of the suitcase?

Repeat Question 22 for the power needed raq coqd5s8ha 6:ther than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb sjd0mwo73lx8m cm i06v traight up?mj md0w83ocx760limv

Recall from Chapter 4, Example -7lw1 k2py /;kq, .kw* ;q:e5tm huztiw lqlij4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for everypwij i lqy*;we k zk/2-l7 hk5:;lt.q,tq uw1m 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 falttpe;w594b 4abf:mdx ls 2.f5 dpx4t;ea w9btb m:480 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How much work dicl/3fr;;uru0lh+ht zy- 9 cis required? ;iclf r9rct-hz yl+u3u/h0;d   J

  A 1300-N crate rests on the floor. How much work is required to mj sufhfgi8 +9,ove it at constant speed (a) 4.0 m along the floor against a friction force of 23gfjs i,f+u98h 0 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crate 10.3lwa52 a/kc pody2,si ( m across a rough floor without acceleration, if the effective coefficient of fric2w,i 5p(ado casyk/2 ltion was 0.50?    J

  A box of mass 5.0 kg is accelerate b56ax - f9so9g f-u6y5tb flmjlad7)fd by a force across a floor at a rate of for 7.0 s. Find the net 7 fmfg6ju l -9tyd) bbsx5af9of6-5alwork done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 ko: .yahu9t r0avgy/,i g, lie flat on a table. How much work is required to stack them 9,utai0y a hrg/.y:voone on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects weic.2ev 3t,t mtk w;3yb0va/lv might not otherwise be able to 3a/ y2;vte0mkltv.3cv, biw tliff. 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 is kept from jmdr4 oshrp2p -mlm j-d7 y8l;y(fr(+accelerating by adf p7lrs-8ljmhr moypy2(m(dr4j+- ; man 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(h4o zc;7 jqyu give a helicopter of mass M an acceleration of 0.10 g upwar4 ju;hc7qoz y(d.    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 dist-ni5 mufidwlge6 :3t98/bke eance 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, actingrfxsn/s2(gvv(6x/ le 3axa4d along the x axis, varies as shown in Fig. 6–37. Determine the work done3r(ag n/l xv/6 4fsa2v( dsxxe 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 4 u*nvol.xi8c h9j 7gia2/qgron 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 oxygenydzic82rg2-5yn1o y rrz/s th 8 bba7) 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,6a0e(mlda yj, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stnag7q5 .k20/rfcu0bwrh ,dd vop 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 tn(q*yt e7v0 +yhjzu b:raveling 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 of 110 quzc 0-r u4e r e81ghic1z1u6g:impj5N on the arrow over a distance of 78 cm. What is the speed of the arr r5uhiecgz: 6rg01q ceup8 iju-1m1z4ow as it leaves the bow?    m/s

  A baseball (m=140kg) /sj 3*v /olmv1buwq -qtraveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caughtw-/3/* bv 1sluvqqm oj. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increor)whr+mw15z8 tv 9w 6,m* reirhhb* mased by 50%, by what factor will its minimum braking distance be increabw r6)r5w 9 itwe8rrm+1,h*zhhm*vm osed, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on db hjfj7c06 ;:btk(dch v,(q oa level road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rkjv7 ( t;( bhhdcj ,bdoq0f:6cainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pi3k+f notr )j y6lvpag04 p,2pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate thegrot,ilp230pn)+ jf a 6kpyv 4 average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock e)7t d /evo g+s7xg4ahgo if thrown straight up by someone who does 80.0 J of work on dg4h ea7tsg /+ o7)xveit? Neglect air resistance.    m

  A 285-kg load is lifted n2wff2 vny(6 xd8s hvxg*n 6fq76 wlz;eh0pr :22.0 m vertically with an acceleration by a single cable. Determinev2 w ;(h z eng2x7l*8f:n hdpvw0qyr6fnsfx66
(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 44yg 1wc)ut.5cs+qjv+h 0N/m How much must this spring be stretched to stor c v)yj.th+ 1sq5gwcu+e 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What ir 1,tborn/2 swi4 xbfz.*whw1lb)wl)s the change in potential energ1l *r4nb ww,b1wt2. w)slir/z)xof hb y?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter ch uz.m npmr0b l+jgtk,r)9k(m.+tkfm 7 ange if his center of mass rises about 4.0 m during the jut+ztj mm ,.n0uk7bm)rg9fr m l+k kp.(mp?    J

  A 1200-kg car rolling on a horizontal suh (:h xu5:guryhy0cs-rface 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 constsgc yxh5-:0yuhu hr(:ant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the gq ojnx s w .qxwtqi +7)xgn4* 9i3*k8k5rucdk9round so it is 2.20 m above the ground. What is the potential energy of thek*)3sdu9kw* qn r oc8i7q.i5q4 jk t+nwg9xxx 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 ym9p9mw :nm -xm and climbs to the top of a 3300-m p n9m-mpx:ym9 weak.
(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/jzdu e 3 l)w3(mqwht9 next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler3u 9l(q/ mh)td3wjwz e marks?    cm

  Jane, looking for Ta:ioaz g5ns43h rzan, is running at top speed (5.3m/s) and grabs a vine hanging 45:haz3g osi nvertically 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 fw 6l/k nz(b1ikrom rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove dwmtbd*4hexp 03 l lb1pcxr/1 )7w2paup 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 ene ooo/1gd d8d/srgy is transformed into gravitational potential energy without the aid of a pole.sd o81do//dog With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically uieqf- nf;n+u ,pward from the top of a platform with a speed of 5.0 m/sfi+ -,fen qun;. ($\alpha)$ 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 stif)ug8mdc a6-jz fness constant is 950N/m is attached68aug - j)mdcz to 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 witgj zdvp:75ri 2hout 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 (whos:vidr2jg 7p5z e radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring a2bd8s) lv sn3stiffness constant k), Fig. 6–40. The block is given anvnsb)sda2 l 83 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 a bridge. She is tied to a bungee cord wm1ixdyymh:1vsv v 47 3hose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’7v:x 4yvymhvi3 1 sd1ms 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 draucssxev0j+6r5dw r5 ;h4qww0 acm 05hgged up to point 1 where it is released from rest. Assuming no friction, calculate the speed at poin jq0c 60h sx0+cr4;wws5mvrewu 5adh5 ts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thr zi58k 1zsq) su6t-(ck06tr :ozyg ybhown with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be plg jt6f+a 62l h:2*dfdoylcc7k aced 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 :g2 6jkfl yc*tf6 aco+dl27dhbe the total mass of the elevator and passengers.

  A cyclist intends to cycle up a, s9jxs cpvjjj1ut/o.op// 3t 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 opposzpbos (.d12fulc -p6 pite directions, collide head-on and co2b1pf. pzus( dpl 6c-ome to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends fv ,-af*vn cgze)6o wd-urr ;ap h8,/ka slide 3.5 m high and reaches the bottom with a speed of 2.2m/s How z, d)pvw/rck fe;h n86-v,*oraugf-a much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and+2jb -9 ljj a 0+uetnplsj-5af 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 treeq qj;*uo.czp9 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 tosn kzd6o7i6 /r gb.u-g a height of 1.5 m.zg6d6s bo7i-n/. urkg
(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 *j-i mj55o zrrfloor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of thoz m55i r-*rjje crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a sp g,lz-ntai .kh/)cpx7eed of If the average force of friction is equal to one-fifth of its weight, with what speed will ihntl.g)aicp/,7-k xz t reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a stea.w-t1ew u6zt w29,vvy5b;uydo dyb1ydy 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 s pcv, o(z8;/y6ageugppring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between theg,zy gco u( 6/pv8ea;p block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig.ye:ln,4fv 9mb 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. I,:4n9l vbmfeyf 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 t/v*p7ihog0e l-o,wfhl-,w sspace shuttle used a “glider” (mass of 980 kg including vlfs ,hp gwt-7eoi/,*w- o0hlpilot) 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 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(k/8(xghsxa+kd0z 5:j bw l fb a 1750-W motor to lift a 315-kg piano to a sixth-story window 1+0(zx8 swhbb 5d:(/agk xf klj6.0 m above?    s

  If a car generates 18 hp when traveling at ollnw 9xzhsox))p n v(a;x (imr8b6it-x,q- ;a steady 88km/h what must be the average force exerted on the car due to friction and air ,iis))zl8x;((xx6h-ovr; na9x qwl obt-pnmresistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is t-m mrbu h; uaop;n-(u/he average power delivered by the engine?( -m;a/urobun ;m -puh$\approx$    hp

  (a) Show that one British hf9*pre ;u:7zt,c 9apj fb2dcqorsepower$ \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 ab; pg9ow:d8. kyz( cbwre 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 he yb ta r19(oj2t*l3pywr 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Ap 39w(*yjb rlytto ap21proximately 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. 3o7+ wwgii*f)y 8utpksh;xcm m7wk 1 motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg p pa;i z2*/xjet8q;,o0ulg yg shot from rest to 14m/s If this motion takes i*upa z ;o/20jg lg,p ;x8qyet1.5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute tu8(5a,ecdche 2so i6z hrough a height of 3.60 m. What output rating (watts) should the pump ocaz8sdh5ei ,6 2e(u cmotor have?    W

  During a workout, the football prhuj08 wly+kr te3/r 1layers at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long a3/r1u +ek l yrjrw0t8hnd 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 cycliz i)so-( . s3wzrj6n hbhs+n2wst 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 st(y-*ffnj/xo yeep a hill can it climb at a constanff( jx*n-oy/ yt speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be ablekkp5vzvk(l l4* ;+llb to drag a 310-kg box along a level floor at a speed of 1.2l5pk4l*k vll k +;v(zbm/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a bvv +dmhnhu-i15f w+07.0 $^{\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 design p3k7b 50knhbg0g:mjt ed 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 bump7 kgpn :0bb03jgtk mh5er 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 grovw/k g cm080gaund, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the averageg/8vcgamw 00k 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 jump (Fig. 8mfidj z3fg+gs3xn + 46–42) in the 1936 Olympics shows that his center of mass rose+n sg43zigjf 83 dxfm+ 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in Ff8bj;ti 6x3 zoig. 6–39 is to remain on tt8 3obfi jx;z6he 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 afterv d7 ewqqi;egk f*g553 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 pilo3f e kggd q57qe;wvi5*t’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 mpn/ mk9/)h- zca20 io+tgke bis fixed (Fig. 6–2 e9t ckgm)amkzopb 0/+hi/-n43).
(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. zwb- ou*;k wxo5-l(mv9mzz n8The climb is made in 5.0 hx59 (m-8 own*wbo z-zz;mlk vu starting at an elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 92rvx:i8 vxql lg9 fr9xb 7fno7 15p.xsa;fz0 i70-kg elevator 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 that its lifts can move 47,n,o9(ok. t .e oghj9vc000 people per hour. If the average lift carries people about 200 m (vertically) higherh ,vojcoeog(.nkt9 9., estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kyy:9ht3o);k smme/ :aekr+pp g/s and falls vertically 81 m before striking the turbine bladestpe3m)/k+:py oyma rke; :h9s. 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 cyx2p7n fgk0t1u.5dcu oaster with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore fr21kfu.0 c7pxug5 ydnt iction. 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 du:t*c, +j-; 6bwmia 3jh3dtz i t2eas2.myfli irectly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=100ul *mt: ;emacd,ihbs .t6j2jywfi323z-+iat0kJ)    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 upwaz )360zpbo5 )vxyxj dtrd 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 bathromd76f -d ,fd/uz uje4mom scale, the spring inside the scale 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 fd-z m/mfeduujd76,4 read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out over a lw/h)r b;n5,nqnp3 gctake (Fig. 6–45). He releases the rope when his vbpq, n/c 3;t 5grwhn)nelocity 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 iai;;fd (yvf5 a vertical distance of 5.0 m in 9.0 s. What minimum power output was usediy5 diafv;( ;f to accomplish this feat?    W

  Some electric-power companies use water to store energy.4mzk9cy;ge8/pk:- d syh5 gi u Water is pumped by reversible turbine pumps from a low to a highgup 5; mdkyc z9e/kiygh-8s4: 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 sprinxc/tpv,g, ;bgv*l*n pg stiffness constan p/x*p*;lc bg,v vn,gtt for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m 5 :qxu*nw8bilup a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2r k 5jqhfl:,t2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the sakfltrqjh ,2:5 me, and neglect frictional losses.    s

  In a common test for cardiac fuq jm*5iv zg/,pnction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when / *izvm5,j gpqthe 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 verticagcbt*mv/pmopp ot: zh 46+39 xlly upward a distance of 500 m, what was its velocity whcb xo*t64g om/3h:tpvp9pzm+ en 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 ms* .d(lc9yncg 9dr zf0b5j0 dwheel from a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximujz 0 0.95c nsr9fg(mblyd*d cdm power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s