In what ways is the word “work” as used in everyday language the same as g p9* 3rieoqj7lvy -uj*(owb0 that defined in physics? In what wa-e (vp u ow9iq*orbj0l3yjg* 7ys is it different? Give examples of both.

Can a centripetal force ever x zq,8/cqs;e oj-ok7t do work on an object? Explain.

Can the normal force on an object evefxcj;z *w*z:rr do work? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she doify d el;rl- 3kst5: /xobn+(gvng any work? If she stopsn/+ yokv;g-3r l5 sfblt:de( x swimming and merely floats, is work done on her?

Is the work done by kinetic friction forc+mq (xup56 f ttof7mg7es always negative? [Hint: Consider what happens to the dishes when you pull a tableco 7mft7txf+5 gqm(6u ploth out from under them.]

Why is it tiring to push haibc;im7rk 86ovzio6.f6)s1wx nrmg ; rd against a solid wall even though you are doing no workgxvi)c b oriir6 m m6.zs on6;;kf18w7?

You have two springs that are identical except thlwecr j)cx64( f fi)a1at spring l is stiffer than spring acerwj1c46i (lf)x f) 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free tokzl6bt 9 g/o;v9 rkw*z slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, vw6 9rkz9zo t ;*/bglkand 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 gk,i)g69tpronk 7 r1wd6sg b0g ravitational potential energy change when you jump as higpg gi6kk9gb ,wsnr)10 td ro67h as you can?

In Fig. 6–31, water balloons are tossed from v xtbdg:ov(6*x4j7 m sthe roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Igxv4j x7dsm b6to*:(vgnore air resistance.

A pendulum is launched from a point that is a height h above its lowest4y 6p 6s0hzoa1yfs f r5i00bsk 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 initr hf4b6s0sp0yzko16iy0 fas 5ial 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 updf ;z i s+qzx.0mpy/7mright on a table. If you compress the spring by pressing down with your hand and then release it, can the spring le sqdm yfm/pi z7.;0+xzave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–ovp4l2fp es81-qml *k33). The instructor pulls2 sp q1po 8v-kl*lfem4 the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water 0 spnv5ixt33 .s 2.uictlxyp5 at the top of a waterfall fallsp0vn.utl.t35i x5yxs ci s32p to the pool below?

Describe the energy transformations when a child hops arog-nh ;37 iq i*s9gug0qb m-mzpund on a pogo stick.

Describe the energy transformations that take place when a skier starts skiing d +bd0*s2avtmuown a hill, btdu0svm 2+ab*ut after a time is brought to rest by striking a snowdrift.

A child on a sled (total s1itdm3 *)het.k8 q2 xh:y aydmass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bottom depend on the ang : qd)tsk2 8eyixaht*ym1d3.h le 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 fallen log in their path rather than stdsxn kx-,7s4(kulri 7epping on top ankx 7irndkux-(l s,74sd jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fired im6:m c9;xiex into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther thanme9 m6;i:xxi c the slower arrow? Explain.

Analyze the motion oc. 1o6mhmpt j98dm l;ou8 ry3uf a simple swinging pendulum in terms of energy, (a) ignoring friction, and (b) taking86o ouh8 .c 3rlm9 dpyu1mtmj; friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its ozkua.f:jt (ns9ow q;* riginal heigu(.t zn *;ksa9:jwqf oht? Explain.

Suppose you lift a suitcase from the floor to a ta(ix r/tf1 48o mjw65hyvzx p)yble. 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 theyow xjz( 6p1ytx mv4 f/ih)r85 table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed ratre0p f7v/n:fwm 4i v0qher than the work.

Why is it easier to climb a mountain via a zigzag trail than9i e gtzy1qqn2uk;5/u to climb straight u e tu5iqyk2z;q1g9/unp?

Recall from Chapter 4, Example 4–14, that you qnf5(v )n5lhpcan use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled npv)5n(h5fql up? Account for this, using energy concepts.

  How much work is done :pu6cj s +b8mwby the gravitational force when a 265-kg pile driver falls 2.80c:68wsum+b pj m?    J

  A 65.0-kg firefightet502c 8lig b,gdt v*zpr climbs a flight of stairs 20.0 m high. How much work is requirg02dgc p,bzti8 5l* tved?    J

  A 1300-N crate rests on the floor. How much work is required to mover*t wm.*))+n o;hxwe nxudb6 d it at constant speed (a) 4.0 mhdrx dn n )b;u)xmw*.+tw*6eo 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 160-kg crate9ko 1h ,yyifhvr)z(j 7 10.3 m across a rough floor without (,91ikhf7jyy vh)zro acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acrosswbb---b uavn)wpm6nop k2 i19 40dcf z a floor at a rate of for 0) cpw z-md96npkwo i1- na2ubbf-bv47.0 s. Find the net work done on the box.   J

  Eight books, each 4.3 cmjxgtl emo.c;z zlpr,j 88vv(:8 dt0 k3 thick with mass 1.7 kg, lie flat on a table. How much wogt z; 8z jomp tj( ,lxl.8d:rev03kc8vrk 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 m v0 3ezm6bhyjtd7 mgmym:l fq)7 7,utl/ /yf*liff objects we might not otherwishmm fzy/u0fd/7 6jm,y3)e7 t7tm*qvblg: ylme be 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° incl-voe1uwge y i jwy(k44fa -,*zine and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is w f,1a kiy4- owz uyvg4e*je(-0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an acc5 nbvy9r p4c+vlhng.p qmt5 )4eleration of 0.10 g un.5vh) +p r m9v 44n5tygqplbcpward.    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 axisvrf1f .k sh1ii1-+0q dlrn797dzsn ypb z4iy5 is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown in Fi2 iqsuskv9b- 0g. 6–37. Determine the work done by this force to move the object (a) from x=0 m tv9 b2iqus-0 sko 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 act+vfnvw e( v:3ss in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, + d3skyg i f8(ptf(:-b+jqoncwith mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what fmt- 3d9 xub 1pxmvf6t,actor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is requi0r oq8 kaw8vqz 4g;1phred 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 105km/h?gjxm/9c;lepz .h + rd6$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired fr: 81 wy:ee(yend w j0p)hre0ajom a bow whose string exerts an average force of 110 N on the arrow over a disd) 10n8he(ajr epe::jy we y0wtance 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 fielder’s glove backwoy g*71aon5 v db9a8ngard 25 cm when the ball is caught. Wg8b nyn1oov a*7g 59dahat was the average force exerted by the ball on the glove?    N

If the speed of a car is i4.x6sf)2y5chu( go3 ttzthh 3losl x8ncreased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s s4s2h3xxz)tthfo5lgh(y8 tu c.o36 lreaction time.

  At an accident scene on a level road, investb o-4 15qhonkxigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?o1hn5-o4qx k b)    m/s

  A softball having a mass of 0.25 kg is pitched at By the time it reaches t5i5 ngswurl.p-* hc,mn- e4sphe plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between th-mp-cr gnp5 l*hs54e,uisnw. e plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straigh6. igst o9b0* nvx3fnlt up by someone who does 80.0 J of work on it? Neglect air resi. *xflnsbn6tgi90 3 ovstance.    m

  A 285-kg load is lifted 22.0 m v1ht1h9*ni 8 q upciy5sf/dd5 rertically with an acceleration by a single cabl9ri81qh5/ s51d ycnptfi u*dh e. Determine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness constant, k, of 440N/m How much kwakkb ,va8vj6 6)g4rmust this spring be stretched to store 25 J of pot a4j,)a8vw6rg k vk6kbential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.24lwp*;6s luq k m higher. What is the change in l kpus;wl*4 6qpotential energy?    J

  By how much does the gravitational potential energyyc *r5ynqpaobf+- gk-.nst. 2d q2 .oz of a 64-kg pole vaulter change if his centeq5.knaoyc-rnz q-..p2 to *f+2y gd bsr of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal eh3h/ 4ep -0cflvm2dj surface has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is0m /cj23efhh el vd4p- the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person li 6idkjh.zoct-fw7e8 s4d:4)e9 qnd nl fts a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the potential energy of the d-d enw.f:) 9qeio87kc 4ltdz6nh4js 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 e jv2klg:ng:g3 n,cuj2levation of 1600 m and climbs to the top of a 3300-m pg3un2 2gg lvj,:kn:cjeak.
(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 2u5xe1p7nxbr.x bgg un. oam.85 unh3next 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 rulunguxux 81..go b. r5bh nmx 57a23pener marks?    cm

  Jane, looking for Tarzan, *ioogp.o3: ffs:ck9a82z ; clob hjd5is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall treb aoifsfok*o9.:;dp8ho3l c2 c:gj 5 ze 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 re) e/uu2fxhkcjkqi0 7s-1 i0zx st, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove up a ;e(/hciko1fp*9 t* ghr6oiqj ,l3vjefrictionless 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 transformed into gravitatml : l:fjanm1smr:lko1z a+-;ional potential energy without the aid ofza m sl1k1o+:j l-m:n:;alm fr a pole. 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 upward from the top of a platform ed1u)y 2ylfc-*i8ni dwith a sp ulyy)ec-d nii 1fd8*2eed 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 spring stiffness constant is 950N/m i5.mepn,q1l,h d9b7aai4n cxke7rv 6i s attached topkc7hbx9,i5qa7 n, 4e r.em naivdl 61 a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track s4ojlfs k2 .ju4hown in Fig. 6–39. If the block is to remain on the track, even at the top of the c ujj2f44.okl sircle (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 con *xi12qrs /ovf4n6t z-bofl9rstant k), Fig. 6–40. The block is given an init/-r4on 96* sivf z xlrofqt21bial 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 j-h 4-;mz1 bbsb yf9ivhf0 w,/,y :ywkrcejq:oumps from a bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the springwfby9ybohy - brz:,jk -q;h,f w 4:ei1c/0 vms 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. 6z+jea ckxh;9tfy)r )0 –41 is dragged up to point 1 where it is releasedra+k0ecf9x)hz )jy;t from 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 pxw q;gcz, vu),d8 a;z16zmyzj(.igam/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 placed at the bottom of an lqx)i puky;xh1 6d(c0 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 0; cikh)dx(1 pl6 qyuxshould 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+veer.y0sx,rw es l:* cpt ;p0.8 $^{\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/vnn bgw1j2hrm 0:j 9u cam .,xjqd.x+0h in opposite directions, collide head-on and come to rest. How much tr01g. x+u, hjb xmdvn9mjq 0 a:w.j2nchermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches thenw1 jqni5ez20 tq+mn1 bottom with a speed of 2.2m/s How much thermal energy due to friction was gene 1n1eiqnt5wz0q2 jn +mrated in this process?    J

  A ski starts from rest and sb6uxeh9iwpg,te*r,9 e8xmu. lides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m ab)/ y 2pkfblm2hove 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)9egptb8w.3j fv5uafxl o 0y).0 m, and it bounces back to a height of 1.5 m. wt. jfl 3)f9e gbpv5 0axo)8yu
(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 constdmo;ax3 39mkt39oupyant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the c 3mo3to dxkp939;myuaoefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in zf z w-qx6mx6:/j3 wagq6q*ahFig. 6–41 passes point 1 with a speed of If the average force of fri3qgqxhfma 6 :x6a -6jwqz*z/wction 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 steady upwartb1 qrgsf4 -lb 6cl19uku*n,vd 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 9vi 3q1y: ld( avagmq5attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40dl3iv 9v a5:ag(qym1q. 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 attachcthkd jb.z7i v+zk81 0ed to a very light horizontal spring, Fig. 6–40. The block can slide along a i.jdz1h k 7c0 tkzvb+8table 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 its first swing?    m

  Early test flights for the space shuttle used a “gli*- ve 6k:uf(1 eapvykfder” (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 speed have been in the absence of (f1ke*afvv - pyu:6ek 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 l3f wh1hkj8)g zift a 315-kg piano to a sixth-story window 16h)1jfk8 wgzh3.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be thew;bvyh/ lq,e8umt 9 o7 average force exerted onuw/me qy9;tv b78ol h, the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What iqm9 + /tbmtp)us the average power d) mbm puq/+tt9elivered by the engine?$\approx$    hp

  (a) Show that one British hor*fz7fipnk te nsrk2 e*;mwsy( ,,d/1k sepower$ \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 unitn9fkmjaild*wi6wk/:z:fa2 3s are often expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 66qx7 nvaql u 1zgnfh94f-rl *45km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car trav 6v- uxzna1lr4nfqq *g7fhl94eling at a constant 75km/h.    hp

  How much work can a 3.05bjoh4*sxlx(yl: 8c d -hp motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motlxa4y-aw 4 ql29/ybehion takes 1.5 s, what averag ywa94ahbl2l4e-/y x qe power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 9bm 5hss;v*bo 2a:wb h3.60 m. What output ratib5b;m vsw o:9s*2hbha ng (watts) should the pump motor have?    W

  During a workout, the football pq 92gdin4rr5d layers at State U. ran up the stadium stairs in 66 s. The stairs r2dgiqn54d 9r are 140 m long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.090 wo +s3sdsjfpx +;ym $^{\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 pomxnkccbt z.,gi1 *d)/ wer output of 120 hp. How steep a hill can it climb at a constan/mc*b1 )in c,t k.xzgdt speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able b0c:59ge 8l pbctnjk*to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of frig5e: pj0tbl* k9c8 bcnction is 0.45?    hp

  A bicyclist coasts down a 7 (wc4g;.ev28 eec4h fo a0sksp.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 ddg :g ;ymgefe5m: 22nl) ur0dmesigned to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a ma umgn)fgded2:r y:0lg5 2m; mess 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 thw y5ek2; a-( fy/ahzdz+iksu5nw wf)4e ground, and the remaining four shelves are z5;w )w+iyae5k zw/ f(uysfndk 2-h a4each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average 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 (Fi(3 n ni.ymlc(yg. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch pointm3yy(nl ( ic.n 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 with)uud,o0sqr 1 qvpwl0;/pwfl nyqt- j+..* fx vout friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loop of.0ll tuqv uj -dr ws+fy);pfq0q/px *nw1o,.v 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 fel68v f+0 tmwyokl 370 m 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 injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s fkvy+0owm86 t 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 wholbmdbso0g + -v n1z(n6se other end is fixed (Fig. 6gon m+ szbn (6b0l1v-d–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountaa e,imqm uh4569kqf: nin. The climb is made in 5.0 9,i 5hqkf 46mun: qameh 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 whentk9 q,*v*kb2b /qpulo 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 /x6z;9be* ph xz9lvmdx 7i9jqclaims that its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power nee9 xp b/ 7d9lejxih m6;x*v9qzzded.$a\times10^b$ W a =    b =   

  Water flows over a dvjl+a/x3w:mn am at the rate of 650kg/s and falls vertically 81 m before striking thvma l:/ w3xjn+e 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 coair.w 51j sfqx/ster 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 friction. Show also that as long as your speed is above the miniq5 i.f/ws rxj1mum 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 e:vhw q8vu7 t:nmq,/i bar directly into work, how high could an 82-kg man climb a ladder if he were fueledq::t/hu mievv7q w8 ,n by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle of 45.0 x-3y flpk j:l5jfjwt qjp5/;c 1uii):$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale x0 g,zn(g/ 7 2bvne.vytzu /slcompresses 0.60 mm, and it tells you your weig/x(b0g2gn.vz/u,y n7l zevts ht is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs atxd 7:up q+*u7dskk-ob 5m/s grabs a rope, and swings out over a lake (Fig. 6–45). He releases the rope when his velo-7d* xkkuub dq pos+:7city 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 athle hfql7.ct yu *yjh*7jmu*lzv**k.0ax(/s zwd te climbs a vertical distance of 5.0 m in 9.0 s. What minimum power7 vs*q z0tyl *(/c.7wzj*f u*jyhxd. lauk*mh output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped bypq labt -s+v;f2ft7 7u reversible turbine pumps from a low to a high reservoir. To t7t-avqb lf+f2;s7p ustore 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 stiffnes4jep9 hmx-b nx+.l5px s constant k is cut in half. What is the spring stiffness constant for eachp4hn5 bx-mxxe+jlp9. of the two resulting springs?   k

  A 6.0-kg block is pushed **hzru)5s;noolq pg0ik2 8pp 8.0 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; . 8q;;zgrddr;ouzlsa; mw5s accelerate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and negaum.ow8 dd zs; ;szrr l;gq;5;lect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patient walks on w po ,g*v1bxk2an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the trea,gv*wp12 o kxbdmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance ortto tnj ll-cn; k+4me7w h,*bn+psq eqa5:73f 500 m, what waseno+cj7;+a7kh* 5e ps : n43ql m,twtl tbr-nq its 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 a hej1yyxb- f5.nbok v) 9oight 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 maximum poweryjxyb .o-5 f1 on)v9bk output?    W
(b) What is the speed of the water as it hits the wheel?    m/s