In what ways is the word “w90zb j 9 wmuvo7g4bou+ork” as used in everyday language the same as that defined in physics?jv+u4bo 90m97uz g bow In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an q :n/*tg m.djyobject? Explain.

Can the normal force on an object ever do work? Eyim+1( qxswk,7 7qe ftxplain.

A woman swimming upstream is not moving with respectes ,c2wq5endti0( xn2 to the shore. Is she doing any work? If she stops swimming and merely floats, is work done0 ,e qen(tsnxd wc5i22 on her?

Is the work done by kinetic friction9k / (*yytv9ujuf c/bf forces always negative? [Hint: Consider what happens to the dishes wu *fj c//(k ufb9tvyy9hen you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doing f ra-jsbyd7n(c8 pk*1no work?nsjy8kr17 dcp-fba* (

You have two springs that ar*7i6j6v jqr *53wgjif 6 oppdle identical except that spring l is stiffer than spring 2 j7pj6ri*6 l* wfi g56pqvo 3jd$(k_1>k_2).$ 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 h+tk7:8 r7u oa2fwtzbeorizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has t8zf ktu+owre7a tb72 :raveled 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 pot7u vdpmt8p c*,ential energy change when you jump as high as you cantm pp*d8, cu7v?

In Fig. 6–31, water balloons are tossed fro8;/huvugz0k qybon 8xh3x) s 4m the roof of a building, all with the same speed but with dik0 h)y8n8xusoh x/ 4b ;qu3zvgfferent launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launcheew;hico. idvu5lqli- 6 x3:c0 d from a point that 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 the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the si5uoivllq03xw ;:6.d- ihe ccecond 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 tab:5gdzbq b8ez ; -nr7ii cr1es2le. If you compress the spring by pressing down with :en58 z-c2s ;eq irrgi7b1zbdyour hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the c)qgx a:: p a3lrxz7i 9rf/(zrgeiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushif 9 /irz37)zrrlgpg:(:axx qang it. Why?

What happens to the gravitational potential enesv:8zv3 puwp k7a ;n39-svz)ue) zo ayrgy when water at the top of a waterfall falls 3an )vey)z :kp;sv8a-wszpuz9v7 o3uto the pool below?

Describe the energy transformations when a child hops aroudp2t h2jqzias55t c;2sp :lf2nd on a pogo stick.

Describe the energy transformations that take place wh i.f;q3e(na a1ff..nw*2 5 klnw8 qfjjyg0pamen a skier starts skiing down a hil0ai1;q. n2n 5yl a j8nfff.qfg(pk*em.3 aw jwl, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) start*e3eg; gfyhr 1s 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 (dhf y1e3r e*g;geep snow)?

Seasoned hikers prefer to step over a fallen log in their path rxzk74w r,+tt3p:i l6ztvrh x* ather than stepping on top and jutx:4rzv6 3ilzr hktx+7p *w,tmping down on the other side. Explain.

Two identical arrows, one with twice the speed of the ot 5u.g 17x (jsu0e vdgxt/lvte;her, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the fas5 01x t(.tjdsl/7ggvu e ex;vuter arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, ug9kh2a aik(6 (a) ignoring friction, and (b) taking friction into account. Explain26gkh 9ua ik(a why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its o4ewd: :sl jzs-umg: 9griginal height:4: sd9 zmejwlu-s:gg? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on thexv 9k6ulx9a nfw3fw7mv/ :+ hs suitcase depends on which of the following: (a) whether you lift it straight up or along a mor7/mxwf kua wv xlf+93:s h6vn9e 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 rathzlir 4 7bjoz,2er than the work.

Why is it easier to climb a mountain f3 n8ch.qswi2via a zigzag trail than to climb straight up?s 83cnh w2fiq.

Recall from Chapter 4, Example 48t b(eg5ao frgcv aqkf qvv1ym65b4,(n, :;y f–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 every mete mfnb 4v, 8k(oag;e5qfc,(b:6 ytrvav 1gfqy 5r the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the,7.h y:.gm7ce mvwsaz gravitational force when a 265-kg pile driver falls 2. m 7yv7as m,.zw:ghce.80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m higuk)79s *awzkch. How much work is required? z k7kc*a9swu)    J

  A 1300-N crate rests on the floor. How much wyqdl00iv0yh w*.gsb 9 ork is required to move it at constant speed (a) 4.0 m along the floor q0.9yh sy i d*b0lw0gvagainst a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kcn:44 ro ()v;(gnfw mpfjx3k 6nwlr8yg crate 10.3 m across a rough floor without acceleration, if the effective :w pjfcmlg(n(o y k3x6wn4r 8)n4vr;fcoefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rs9q i0,5 5-( zwbxlv(b ymnnwcate of for 7.0 s0 vn9-c,iwm bzy(qwb5s5xln( . 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 dg+ um;1,x*af :bj bvdmuch work + xfgma*u1 ;jdbbv :d,is 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 objects we might qg: ircahe25)hn 2l h9not otherwise be able to liff. Show that the ratio of ihr h q25n)c92l:eahgoutput 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.o9qe;1xz k,yed96kr p n8wrr26 m down a 28° incline and is kept from accelerating by a man who is pushing back on rzqk rwexk6 n8o,rp1;d2e9y9 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 helichy. -coks+0 bgopter of mass M an acceleration of 0.ohybg. +c k0s-10 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is linead4( wsj cgf)*emagq d g28)p)nr 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, a-wejy:h n e3m2cting along the x axis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from xnw:-m jehe3y2=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 ing bi ytxer,gzh0r(8q :zq*, o8ur2,wn 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 ox d)b8ixf,d2 f/*ks bqgygen 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 doublllv.u)n6 8m* lora9 caed, 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 d 8np9 mqjmy8: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 travacsa o9t+t 4b2eling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose strinq;u4 e3mem9w 2luun7 sg exerts an average force of 110 N on the arrow over a dism ;9uqmuwunse 34 27eltance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fieldern y qk)y2xr kr6+pgkhqnf7/hqeqx84 b+ j69b*’s glove backward 25 cm when the ball is caught. What was the average for)kf+*9626jqbgy xhn8/ r nrq+ kkybqxq47pehce exerted by the ball on the glove?    N

If the speed of a car is increased f3b ausdht.3y .pk /:wby 50%, by what factor will its minimum braking distance be increased, assuming all else sb.k p3/d t:afy.whu3 is the same? Ignore the driver’s reaction time.

  At an accident scene x+al8v2 dt9ej on a level road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient oda 82l 9+xtevjf 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 ,-e r:pt;uiptti-)nwm ydp/o sw.8 4qmass of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate t, w.qrpnt4 opwiu-m: yie8p/ts;)-dthe 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 go 57j6i-(jfx -t fcozhocl7uyd/)n 9 +aorvxc2if thrown straight up by someone who does 80.0 J of work on it? Neglect alxyuc+h9fx o6t- a/ ivno7o7c)(25c z j-fjdrir resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single x9;zzceddnknf1-8v/ upp. n2cable. Determik1z ;en.nf9vud 8d/ pc2znp -xne
(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 How,ceso+e o/y erh0n6v 5 much must this springye6, se0/+ h ro5vecno be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What w m. 4yib,wvdp+ 9cfqr 55n:cnis the change in potential5c4 f wp.wm+i, dnvybnq:5rc9 energy?    J

  By how much does the gravitational potential energy of a 64-kg pom(8mrpvn9 2 ;0i s7jfzq j+xpmle vaulter change if his center of mass rises about 4.0 s+jnjfx(q 80p zi927;mmmvp rm during the jump?    J

  A 1200-kg car rolling on a horizontal huvxh-ehzffak26 a 6c1j3; 0 isurface has speed v = 65 km/h when it strikes a horizontal coiled spring and is broug a6-ex6f vaf0h3 z21ihk;cuh jht to 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 jy 9c+.aulx( d2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the book relativeax9 +cjd (.uyl 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 ek 10pm-vqk5n t*iux6rj/g i4yet5 f-top of a 3300-m peak.k6iv5t r e-yi1 gqmt /pf*-4nxuj0ke5
(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 mhg 75bqgr7 )tvertically 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 wiqr7 mg t5b7g)hth the ruler marks?    cm

  Jane, looking for Tarzan, is running at top spq 2o + juwls9z4lt8z;jeed (5.3m/s) and grabs a vine hanging vertically from28l9+jo zqlsu 4wj tz; 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 rthy6d qb2,d:ry0k q/;3 l8knoo ; vch4drjki3est, 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 gi wpdob0 /lsa)x3 ee/1sven a shove up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is tranod9tsoqvq*: a a5 /vx0/ r6 7ibwokck9sformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her centedx: a *vc0ikoq/so75qotba9vr 9/ 6kwr of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from thv53-m-g1 o9wrm iqgdze top of a platform with a s5ogi 1m-gr39w qvd m-zpeed of 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose oh,;l /mb z e(z*yseqh wk.0y3spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upsz zhq/mlhb.oye,0k w*;3e y(ward 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 along the looped tr*:)pb szekfaka ysf3 :n3h: 2back shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it n zhek:asb:bfya3)f3*2p s:k be released?    r

A block of mass m is attached to th i)i81fzz2(ymbvfs ist*-6-ggm- x lpr7s g4 we end of a spring (spring stiffness constant kix 6g f7m4821l ir*sfzsvi-sy)(zpm--gg bwt), Fig. 6–40. 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 a bridge. She is tied to a bungee cord whose60e) ttqt.*pw0euy6nrd.iy -bb nm2 f unstretched length is 12 m, and.bir-0nb6e wt2)p*0yyu6fd qmtn te . 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 where it i26/ :o fyu qtpum+nau8s released from rest. Assuming no friction, calculate the speedftu 6uu +8a2om/nyp:q 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 om;ut7 doh8 n kxxl8)t *)x.czgf 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 pl hjdf -wo-.y.laced 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 undergojh ly. d.-o-wf an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to s i 6z5rd8 odwfoq.-1(umnn2vcycle 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/lkbp/dm r f9.+h in opposite directions, collide head-on and come to rest. How much thermal energy is produfbr+9lk/p m.d ced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m eeb /6d 0gqi1bi +o)zdzb-p3nhigh and reaches the bottom with a speed of 2.2m/s How +/b6 ei1o0 d qpe bdig-zzb3)nmuch thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides e 6l4-ff4 dfx74gp d8:mlcty z xr9;hjdown 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 dropb ,t-o 9ov8whiped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, andowkfx p72/-yiq oly(- it bounces back to a height of 1.5 m. (y7 o xw lko-yq/-pif2
(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 constant hory -2v: v;hjtndizontal force of 350 N. For the f2d;y-htj vvn: irst 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 the crate?    m/s

  Suppose the roller coasp :zk uz1u1vk1ter in Fig. 6–41 passes point 1 with a speed of If the average force of friction iuv 11k:k1puz zs equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a st bs qy(67y;n(fkuxk; xeady 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 attct:0p)v eql bcidcn 7 v1b27s(ffv6y8ached 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 released, stretches out 2.3 cm beyons68 vy dfbpcflbc )10:vqt2ce nv7(i7d 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 attacb1cdg-dy; 2f z5 l 5n (1eyhya3m-ipmkhed to a very light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how fp5mfd3ebczgk2y mhl 1ynd; 5(y i-a-1ar beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” 9inlsi*t)* tn (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing sp*i9s )ltni*nt eed 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 lifwf9z1,)dspql 7z sqy- t a 315-kg piano to a sixth-story window l zqzys1s9d, 7p) wf-q16.0 m above?    s

  If a car generates 18 hp when travem .sw,nf2icm* wl/8 xbling at a steady 88km/h what must be the average force exerted on thlmm,fcx.s* /bw wn 28ie car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h dt 1o:4cr mndsh- 2ov5khj ./win 7.4 s. What is the average power delivered by thr/wh: doct1-no.5 2 4sh vdkjme engine?$\approx$    hp

  (a) Show that one Britg;teulz4o 0za+nv ,q mx 9c61ftl n/j6ish 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 units are often exp(e*:u0u-k drbl:w ik ,n6ker wressed 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 down from to 65km/h in abou5vu ychcm 4khi4pr:gt0-nq m/65.9 s)u rf fjrt 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constantg:0h rqt5vi.kp r4 yu6 /hc c)sm4nfjfr59-mu 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h?r64 d29:wqzamg as+d*+ntexs 1lt0h m $a\times10^b$ J a =    b =   

  A shot-putter accelerat,bemlx . r)t)qes a 7.3-kg shot from rest to 14m/s If this motion takes qxe.rbml t)),1.5 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of fm5. ,lev us-nwater per minute through a height of 3.60 m. What output rating ns ,.me5luv- f(watts) should the pump motor have?    W

  During a workout, the football 2iq edxzz2 p3;k f1a) u4734iwgfhg; oe9khshplayers at State U. ran up the stadium stairs in 66 s. The stairs as2kfh )ha g;o wk2ix4 ude3h394qe; pzi1gz f7re 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 cyclbqsz xe0nx gbu69j7uw: + sz*,ist climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How steep a hill canmx w ic0*w.c6n it climb at a constant speed of 75km/h if the frictional forcewc*0m6xwnc. is add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able tz3a 7/abtdop)lv) u o ylg*6mjbr20 6qo drag a 310-kg box along a level floor at a speed of 1.2m/s if the coeffi3odb60zml7jtbvrg pq6y)uo* a a l/2) cient of friction is 0.45?    hp

  A bicyclist coasts down a 7t n8u9sci gte; 6ti6+x.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 designeazu2h i,vaw-u;gudw qwh .v t3 ,yr*74d to compress and rebound elautvv rwa;q4yh-uu3 7g,whid, z. w*2 astically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf isujv(09ycos2c5btx c) 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above thecy )u0sxtvco9 b2 j5(c previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famou2 5 z xxthjx/elw u(ddhp*)(9 0p5jtffs long jump (Fig. 6–42) in the 1936 Olympics shows that his cent25e f (jp9x0/*zx5xdtw( tp jhf)hul der of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the loopeasiwkj9 n,;mwb;dvc(/1tyzd cc)g/n;:y l n +d track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of thekczavi y9:nc / +1t)njn; s; dmyg ,/b;wwd(cl 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 mhuy)6 ijpiygf:z1ybds-;3 h ; after 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 injjpzi;s:u);idghf6 yby1 3 -hy uries. 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 mfar8yo xe)9n +-3pcjcord of length L whose other end is fixed (Fig. 6–4fa+9) 38-ne yrcoxmjp3).
(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 j:hsio/k +n9x x9fv6k/kcec ,3700-m-high mountain. The climb is made in 5.0 h starting at ihfn9:vxx6c kkoek c/s +/j9 ,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 brea(.iq8zpq3 cqe n(t5nw ze95cz ks when a 920-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 claimsgm+ )gbz:sf .f21l;z 6kpmj kx that its lifts can move 47,000 people per hour. If the average lifbmpg;. fs1f) kj2xk6z+lg mz :t carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertically 81 m before s , 0ndnm s+vly,:3,i zd z.jsit2ztj(otriking the turbine bla td2jvosizsm0,lntj: +3n (.z, z, idydes. 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 alv9ef-7o8* hh pa3vb4b - gwbw circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and th7*89-of wwbh a 43e gvbbvhp-le bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into work, hgr67 w.bc*ibmow high could an 82-kg man climb a ladder if he were fue.rbmb7wi* g6c led 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 up /pyi+8k a;iv1 a)wudkward 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 /9blcf dw58va 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 read 59w8f dl/cvba at its peak?    N

  A 65-kg student runs at 5m/sihx.7a/ 9ba)iv5 pz tx grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope wb.xhxai5tpz /av9)i7 hen 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 a vertical s.a0wtc f t-lh7.mp,qwsyg50 distance of 5.0 m in 9.0 s. What mt,yh pf- sgqa 750w.lc.t smw0inimum power output was used to accomplish this feat?    W

  Some electric-power comp 0wz53 o liafd-jcl)x9anies use water to store energy. Water is pumped by reversibolw9fladc 5j0 3 z)ix-le 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 sti ii7c/kl )xk/p qi0nff9 dsg88ffness constant k is cut in half. What is the spring stiffness constant for each of the two resulting sprin/80xiln ksik/if8 7p g9df cq)gs?   k

  A 6.0-kg block is pushed 8.0 m up a rough + yvjd vccwbt52:d ;.e37 $^{\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 3.2 s, how l c /sd+r+vto1)l.b;/uba hqziong will it take to accelerate from 55 izhrq/tvlb+cd+1.su)o / b;akm/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks os. cw (y2dom.kn an inclined treadmill (Fig. 6–46). Estimate t..msw y(ko d2che power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a ks o(az6ia. -l*v ndw5b) v5re500-kg rock vertically upward a distance of 500 m, what was its velocity when it left the volc6 .wnzavel5 (a)odrb-* vks5iano? $\approx$    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 height of 2.0 m at a rate of 95kg/s (a) (tzc vnbz1)/g If this water wheel is set up to provide electricity output, what is its maximumzzg1ncv( t)/b power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s