In what ways is the word “work” as used in everyday language the same as that dexq *xhy-lr42x fined in physics? In what ways is ith2q y 4lx-x*rx different? Give examples of both.

Can a centripetal force ever do work on slf 79 3*nia stmyne45z tzk),an object? Explain.

Can the normal force oy *u*w(:pr( f)vplm rdn an object ever do work? Explain.

A woman swimming upstream is not moving with respect e/eldt r:e+s5to the shore. Is she doing any work? If she stops swimming and merely float +/ds:leerte5s, is work done on her?

Is the work done by kinetic friction forces always negativ1 (88u,ko ohegx e javj d;e* hh9xihr-f3:zr)e? [Hint: Consider what happens to the dishes when you pull a tablecloth out from unde eho1fag 3;u89(oxh zev, 8* d:i -xr)jkrhjehr them.]

Why is it tiring to push hard against a solid wall even thou psqqv5 +lr.v:gh you are doing no work5 :r s+vplqvq.?

You have two springs that are identical except5: jc a1uzl(hsvx c2z; that spring l is stiffer than spring 2 (z 1h sx;lcj5 2v:azuc$(k_1>k_2).$ 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 freey rzf / ;dc ,(p::ofvgv2oar;zg z0j,f to slide on a frictionless surface (Fig.6-30). The block starts from rest atyfr :0jzpvf, og(;vg;zd, rzco af2 :/ 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 go74ix y4 ojozeps;-/k 7:t a 9tao0eychange when you ju0ez4 y o7yj a p akis-/oxet;:o4tgo79mp as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all 8 kuccvb0d xg2 qe((a9e o 8/h1gijm/wwith the same speed but with different launch angles. Whicbc(jamo(dc 2 90/eh/ v1ug8i8e qkwgxh one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a heigfkjob;jdva i4f1/w18 (go4fa ht 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 second launch it is directed downward along the trajectory. Which launch will ca(4wvaofd; ag/jf1o kjf81 i4b use it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests uprig yg6e3pv -yxnx3v 18vvht on a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of 63vyvxynvep -1g 38vxenergy.

A bowling ball is hung from 6lk/f auhj4 yy/-fph3km4jo:9mexl ob a4k9 : the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against 3p mlexlyk 69u-fj aoo4/ m49: bfka:/j khh4ythe wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational3ip;0pdf:rq rka50z k potential energy when water at the top of a waterfa zf5p ;3rp irqkda00k:ll falls to the pool below?

Describe the energy transformations when a child hops around on a pogo s f x8(nqp99 v;1ulpvbktick.

Describe the energy transformations that take plg k(pk*8t lc(eace when a skier starts skiing down a hill, but after a time is (8gkcpe*l (kt brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of xg it;r )f3k--k6gyk ,b,n yuva hill of height h and slides down. Does the velocity at the bottom depend o t-)g xun yrfy,k;3,ikbg 6kv-n the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a ffbgy 7w0+yjzu1 5 okju06bk1gallen log in their path rather than stepping on top and jumping down on the other sidw bju yg51byo 100g7fk6+ ukzje. Explain.

Two identical arrows, one with twice the sv1 jr v zw;u7jg53(a evzd4m9dpeed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than tvmz 3d1a v d7 ruz9vj;j(gew54he slower arrow? Explain.

Analyze the motion of a simple y- tmzq. 40kyulv7k zm6o8(vqswinging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wounumzvo -0yt 8l.m k6(k4 qy7qzvd up.

When a “superball” is dropped, can it rebound to a height greater than i/t+mf0cww8b+xzh n 2 s1 6uk-t,d gryfts original heighth+z b +wm1kufndyg20/,8- rcxf stt w6? Explain.

Suppose you lift a suitcase from the floor to a table. The wor /c66b,3h hwnjpz/ i5d8qafhjk you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more6a/bp,wzd q5n jh/ jh3hi8f 6c 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 rpnucuq1 p.r8+ ather than the work.

Why is it easier to climucm cjkl*ws99:oa )c +dx53x2brn-rqb a mountain via a zigzag trail than to climb straight up3cr-x)c+k*5s2 n9xw rlmqub9d :j coa?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to d) s6v umtfl-(necrease 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 n6)u- sml(tvf for this, using energy concepts.

  How much work is done by the gr,h36skkt m9tgavitational force when a 265-kg pile driver falls 2.80 m6 kghtms,k93t ?    J

  A 65.0-kg firefighter climbs a fli amnbzp8u k-sz,i8-1 ight of stairs 20.0 m high. How much work is requir8p- z u-kna,i8b1mis zed?    J

  A 1300-N crate rests on the floor. How much worxiek h zha6:a64e,f+ mk is required to move it at constak:z ehh 6am4i+exa ,f6nt speed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 16dm 2a8;i .bt f4y6fgtb0-kg crate 10.3 m across a rough floor without acceleration, if the effective cg 4.ydbm b28ttf af;6ioefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acceleraswv8 ch:; rj6dted by a force across a floor at a rate of for 7.0 s. Find the net work done hrsw jc: v6d;8on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How muet7f r y,7aawvmz;y** ch work is required to stack them one on top of anothet y;*7mzv ay*a,w rf7er?    J

A lever such as that shown in Fi jfj ht40jitr l;y,;jbnx+6i6 g. 6-35 can be used to liff objects we might not otherwise b;+4t x;iljj0hyjt j,ni66f b re able to liff. 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 acceleratqs-7z m;g is hm ;qj).yq;ltl:vj)l0 iing by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0 j0iss7q.-)gj)ym;;vh i;qzq:tm l ll .40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass Mhl7jggv*/+4* gs ksqavm74 ru an acceleration of 0.10 g upwarq krg* vj4a*47l+vu ssggm7/hd.    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 dv2ywza-1 /g plistance 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 objew t -pyk 7i*mj.+jd5qpvu .a*qwmb);a ct, acting along the x axis, varies as shown in Fig. 6–37. Determinwab qp*k5vt w-j;p a. idmu)yj* m.7+qe the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts in the /bc1hyvwy3k/2 k 3k ld$+x$ 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 oxygcs0l3 kn3kym n-qf3r 9en 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, b he;6dm,mm(2 ibfu6weq g;p -ly 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 requiregcp5)5lua, v *-fimmi d 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 traveling at 10(5d cm72:)rdat2g- b -t 6mqjl2xzh 7 ivousbw5km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a boi8mnf 2m0wt xf* jeg( i1yuda77, rym4w whose string exerts an average force of 110 N on the ar1y m7j dtgyf2miim0 w (r78f,4x* aeunrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) gziu07 u)g uk7traveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught7kug7gu i 0uz). What was the average force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by whafu;(,/rl+yh k8ng0nyodi+v l t factor will its minimum braking dis do+,k;r8 (ul nnvlgyi0/+hyftance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level roa+ed4q/viw qs3 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 fr3w 4qqv/dei +siction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time i 5cs*.vaku +eat reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the usa5 .*ekcva+ pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by s t(05e htc:tg wyc1sqae9e+z: omeone who does 80.0 J of work on it? Neglect air resist(5:1 ccsaezt:9wtt hq+ y0egeance.    m

  A 285-kg load is lifted 22.0 m verti+. p,hx +gz5o*;vfkakkhzbz, cally with an acceleration by a single cable. Determine + ;,a k+ ,xfgvzz*k5b.h kpzho
(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 440gpj g *3x7ob9k.- onfkv ,le m8 bkt.gj7ctq;1N/m How much must this spring be stretched to store 25 J v7cjgo8km3*.e-,7kq1tgjxpt bkglb f; on 9.of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is thc h*jd wgh (i 3k1vjr:yub++4fe change in po1j khf+wj4ci +:brh*dvyg 3 (utential energy?    J

  By how much does the gravitational potential energy3ufai 1 zgh0p yoka-97l1im8c of a 64-kg pole vaulter change if his center of massay1fi-8lz ou3 cmp 0ih179 agk rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 k/ hxci5tllp-*m/h when it strikes a horpci h/ l5xt*-lizontal coiled spring and is brought 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 2.10-kg book from the ground so it is 2.20 m aauw-,tm 5gvm 8bove the ground. What is the potential energy of the book revgt58amm, uw -lative 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 cvvl/7 e vqq1dk(*idb97rt 2a ilimbs to the top of a 3300-m p 1klvd7*tir a(b d2vi9qv7/q eeak.
(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.sgur/)q.ewv a3n0 t*g 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 ruler mne.0/g )g qstvwra *u3arks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine haus* x4 +fq2yfwnging vertically from a tall tree in the jungle. How high can she swing upward2fx+ 4 ufqwy*s?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless 35.u9ma; c n6owh+:ciov .0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a frictionless 28i8- nql(b7wcd.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into(u x79vc bx4sb0-a c rkxw6 hs)dkxy/3 gravitational potential energy without the aid of a pole. With what mhy s x 4sx/cc(7 bx )r3v0xwb-9ku6kadinimum 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 upward froujo85akmin 9 h5 jt*c7m the top of a platform with a speed of *cj5tjmko 78hu59na i 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 mas 1mq0nla. ndsq+x( +5d awc,tts), whose spring stiffness constant is 950N/m is attached to a tab +wa5q.ax+d0l st( n,nqmt1 cdle 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 withoy s0 .rk:v/a m0ib9schut friction along the looped track shown in Fig. 6–39. If the block is to remain on the trass mayi: v.cr k09h/0bck, even at the top of the circle (whose 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 stiffness const3 ubz641z*e6ylt6bqbz (x sa,nnjr:s ant k), Fig. 6–40. The block is given an initial displacemb6: r,qza6l4 *6 tbxze s(bj13uynns zent $x_0$ 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 conbyj(9m *t .-blmi 2gbyp.pz ,o-pp8hrd whose unstretc82b-j(,9.zy. tbompppnl - mib *gphyhed length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1 wherq iw;(c +aiiz5ej8 ve,e it is released frozi, 5;a8vi+ w (ieqcejm rest. Assuming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at an a1hzb ku/g- hy2ngle 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 placed at the bottom je8xf )4izt1o of an elevator shaft. If the elevator cable should break when the elevator is at a height h aboveo i )84eftjz1x the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.dnwprrb d 98k+i,xl/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 78-hi3 kkmpu jgzwkcq5 du7x5+ wz k5*-650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced inu m5- g5 p-q uw 57wxk8kz+k3khcid*zj this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descevh8yxc zth+k- 8y. 1fynds a slide 3.5 m high and reaches the bottom with a speed f 8kytx hz1y+-8hc.yvof 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and:c9 jcaqmh.0;9itc tn 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 frmca ,d5 7mkq5a+9 owejom 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 tybhki-:h.w)6w(p)af5 j z z e2.0 m, and it bounces back to a height of 1.5 mh(wzew j:6a .5f- p ))bkyizth.
(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 floornbm//vntwegx s;gqx4.j/ *0 m with a constant horizoggvmx *0n/b;sxj m .nqw e/t/4ntal 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 the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a spy m7ip f66xq3jeed of If the average force6 36 mpq7ijfxy of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot of a s*smk3 x-x;se ateady 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 (k=1omho(3,c2v 2kw;surzz3+ k fd80N/m) as shown in Fig. 6–4rvs2zucz fo h; +3w,kko(32md0. 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 the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, z/cb:me)qk2df1,e hc,a* c imFig. 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 far beyond its equilibrium position will it stretch on ,: mz *keh 2c ,ce/af)qmbid1cits first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 kg includieb metzh9* dqas,qr,3c 791qm ng pilot) that was launched horizontally at 500km/h from a height ofq3 9bstq9e7mrmq edcza, *,h1 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 a 1;cmc 4ry, 7vx fpy1n+g)qe +my750-W motor to lift a 315-kg piano to a sixth-story window 16.0 m a4 v+r1ye ycm ,g7nyx;+mc) pqfbove?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must j)zfi k je;gtx8p679you u;g5 4r:kd .zv:krzbe the average force exerted on the car due to friction and airu)67 z4rt:.8d zv9yezk;pfgik o 5rj:ux; jk g resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in f-ec 4 i (rl-w.0ljq(sfdla;x7.4 s. What is the average power delivered by the s.id4- l(fxwf;r aj (0l-cle qengine?$\approx$    hp

  (a) Show that one Britifod m* bp3zw3 q8(a8vush 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 expressed in the form of “kilowatt-h6mkijvsaqjv(57y 9)wours.”
(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 in4u 5jd ; duvaa7nvq.j9 about 6.0 s on the level when it is in neutral. Approximately what power (watts ann.a759q;v jd4j uvud ad hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp chok 82:abv7nmotor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg yplnlfs .pztf4;pqy1/: dq84shot from rest to 14m/s If this motion takes 1.5 s, what average power was d yd ;sz4pq/qff1l.n:p 8p4 tlyeveloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minu (tun /ypdmf7j.(3j thte through a height of 3.60 m. What output rating (watts) should the pump motor have?(jh(f.3j ttpy n7/mud    W

  During a workout, the football players at State*l1fnz bz051ibujf+ s U. ran up the stadium stairs in 66 s. The stairs are 140 m li1l bsjzn z10f5+bfu*ong 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 cyclc.2*jge(3o96pcvu lncd .uzyb,xb3 yist 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 p,.ymb;mx3buy l0f,fpn ezwjk xg 13.0 e(tvc-ower output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up k0,m ft .n;3z 0e 1cuwel-mbxfbyjp.g,3 xv y(to 650 N?    $^{\circ} $

  What minimum horsepower must a motor.lxk12 sdh oixm6kl:* have to be able to drag a 310-kg box along a level floor at a speexx.k 1:lis m62lodk *hd of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0*t9 1zkj6 bt()ceo4gtadft)i $^{\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 havzq6 ;.wf+*bun g wpuq7e 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 permaneb*qz6.uwwg+ pfq;un7 ntly deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm offqt ob 5*de )mcw;+a y9w*cd+qq p11jyb the ground, and the remaining four shelves are each spaced 30.0 cm above the prevd1ca ;)j5qw 1y*w++9pqbdetc* byq omious one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig/b e 9i5u rjkcc-dr/4c(-hm zvtkft5.. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the to.dtk-u k45t ec5 jc rmz rc/v(h/b-i9fp of the arc?   m/s

  The block of mass m sliding without friction along h vk .b0owtt-.the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top o.wo 0thv t.kb-f the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after pgri9 q0gz,760 jwgtx 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 injurqpg j0izt9x ,07w 6rggies. 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 co2v3;ht qk0k4jrmzqd/4e )r L whose other end is fixed (Fig. 6–43c44v ord3 rhkktjq2)m0;e/ zq).
(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 of2xpxg b(o, sjl4cf05x a 3700-m-high mountain. The climb is made in 0b(g2x pj,x cfsolx 545.0 h 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 920-kg elevator is 28 m m.(0ev3jh )vrg+ qx erabove 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 i+wr) v (,o7 kbj6h sbt5zlkxw cv54/ctn California claims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power n, 7xvsz5b ch /wt+ov5 bck6kl)twr j4(eeded.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls vertio s(qgx, h4,ys9v ) -t,aiwhgacally 81 m before striking t,itxv,sa oa) g-ygw( q9sh4h,he turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circu +klvqn9 c-kl0; ses;ilar 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. Igno9sics-q0ln+kl k ;e;vre 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 directlynpz 4c0ui k,q4 into work, how high could an 82-kg man climb a lqcip,404k unz adder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired atq 2yd,sijg 6yon e364q 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 ikaqp cdkar6oa4q-8/. / j n2qwnside 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 do/qq /wq-opjk264 a.a 8 cadnkres the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out oveyrg5f6;;-tveq: o lk ur a lake (Fig. 6–45). He releasesklre;t-o :f vu y;56qg 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 a vertical distance of 5.0 agsni0u4v/5 km in 9.0 s. What minimum power output was used ts5 kuavn04gi/ o accomplish this feat?    W

  Some electric-power companir4,a;8 r x6 o 9spbfomc7ttww92ncby: es use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the ener49 n9 m;8opwtrb2 ,rs :xw6obacty7fc gy 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 smdoqou ).hak hlcw ; 0h5b :lezsx96,2tiffness constant for each of the two res) l.al xuwoh h5 h6zmod;,9b0:e2kqc sulting springs?   k

  A 6.0-kg block is pushed 8 o6/7 fbs(jutx.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long5xav2r 9mbai e lywzv3+8 (xu5uz5z n* will it take to accelerate from 55km/h to 75km/h Assume the pow5zxawvn el*r2 zy(ai5ux v 9 z58m+bu3er stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walksz33ug )pzt ji/ on an inclined treadmill (Fig. 6–46). Estimate the power required from a 7/3tzzu)g jp i35-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 500-kg rock n x(333rx gi e+ dvw/j/jyr7yrh 5,sqxvertically upward a distance of 500 m, what was ijxnvij7gy3+eqw(sh/yx/3,53 dr r r xts velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from xu 6m-rx p(fc8a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricit 6rcp8x um-fx(y output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s