In what ways is the wo 3iqrflpvfo3(s q9)9srd “work” as used in everyday language the same as that defined in physics? In what ways is it dif )slqsffr(p3qov9 i39ferent? Give examples of both.

Can a centripetal force ever dok/ eog h5k;*pl lq8v9t work on an object? Explain.

Can the normal force on an object ever dohccco+ 5) brnt7/i cf2 work? Explain.

A woman swimming upstream is not moving with respect to the shore. n6oaik9 4glp8Is she doing a a9olp8 gn6k4iny work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alwa du88nsoq y 4q /)6*methebgrl3 twi3/ys negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from u6/ew q8be/q dy*8rtih)g3 tn os3 ml4under them.]

Why is it tiring to push hard against a solid wall even though you are d ,t*rhfsin -y)oing no wh- rys*n )if,tork?

You have two springs that a a3zwx vfp)(dnx8b72oh fg1h 4re identical except that spring l is stiffer than spring 2 ff o(dahv8 zh)32x4gxnw1pb7$(k_1>k_2).$ 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 to yi/n3 b,dt zlfg,9u-w slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has traveled -w/3 d9bn ityf,gluz,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 d4( en( i hp45oufrh.v.tnu.jyoes your gravitational potential energy change when you jump as high v.yj.n (riotp.u5n fe 4 (u4hhas you can?

In Fig. 6–31, water balloons are tosse4dspmo)d2 jf(d from the roof of a building, all with the same sp2m fsdp (ojd)4eed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowest point itmbjlhc y4w4):z8 oxz r+g6( ln 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 vco4 8lh rmy )4w(:+6bzg xlzjtelocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress3g;sngdx o/x1 the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation ofogs1;n3x gx/d energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33).sr bi8no,78bq The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed n s 8b87,biqorto release the ball without pushing it. Why?

What happens to the gravitational potential energy when water aa mf0x.,4j7 qjmors4qt the top of a waterfall fala4o, qsm.7 0mr4fqj xjls to the pool below?

Describe the energy transformatio;hx-jytym :p5ha g4e1 wr .7 mwltzt0lsq8;. ins when a child hops around on a pogo stick.

Describe the energy transformations that take place when a skier starts s;ogl-.owntlb1 / p5kwymx7vw7m0t z1 kiing down a hill, but after a time is brought m wwv n 1-zolk/pxog7yl7 ;0.m1w 5tbtto rest by striking a snowdrift.

A child on a sled (total mass m) starts from reedez+ y3,7bpfst at the top of a hill of height h and slides down. Do,+zpy3 b7efd ees the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step ov/i t3mz3y53 05gz 2wblm iowzper a fallen log in their path rather than stepping on top and jumping down on the other side. Explain wb353o iz2itzw/0m zglymp35.

Two identical arrows, one ok ;7k7stv+p kwith twice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional f7k kspo;+ t7kvorce on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of ener lqf3,w 2m1dxrv r u2c7d41iwzgy, (a) ignoring friction, and (b) taking friction into accountrci3m7d lxv d1q 2,u2r4zwf1 w. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height guwpev)co: 1o844.bf3 g3yldzctu g n1reater than its original heiutny 41ec.cg1o8 zlb:3wudf3gvp)4 oght? Explain.

Suppose you lift a suitcase from the floor to a tak7lkous ;mx. 5q.t :i-v vvnm9ble. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more compli:9msn .t -;7.vkxoq5lvvmik u cated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the -lu w 0ixde 5tu21+sknpower needed rather than the work.

Why is it easier to climb a mqpr+a*qn6 bh )je,ee :j7sni2ountain via a zigzag trail than to climb straight uen h:naie)jprbq q7*+6j s,e2 p?

Recall from Chapter 4, Example 4–14, that you can use a pulley and ros (a;.(j/at3qri yv hxpes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account ;is/a.j(rvxy 3(qath for this, using energy concepts.

  How much work is done by the gravitational force when a 26: (jbnt -iechqk-,7ds5-kg pile driver falls 2.80 mtein7 bk,-(: dhcjq -s?    J

  A 65.0-kg firefighter climb y 6jgi,ga))vr 8/qkuzs a flight of stairs 20.0 m high. How much work is require/ 8yiv,kj) gzu)a r6gqd?    J

  A 1300-N crate rests on the floor. How much work4msg aj/zete s-99e7 p is required to move it at constant speed (a) 4.0 m along the floor against a friction forceas jp/74e9e-stze 9gm of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a;xpk0xz,k z,tza8 pu;(ulj x8 160-kg crate 10.3 m across a rough floor without acceleration, if the effectiux,a tlu8k0zx j ;zzppx8, ;k(ve coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a/.e1wnhfv,at 0eski z/t+iveh0lz /* rate of for 7.0 s./ezs 1ea0k/t.twfvi lznvh0e/i *+h, Find the net work done on the box.   J

  Eight books, each 4.3 cm thick wit6t s 6n3e mlhm7-cjrq5h mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top of anothemhm 36l7n56jet srq-c r?    J

A lever such as that shown in Fig. 6-35 can be used to liff objecf() 6-wi,ovp xael:vu ts we might not otherwise be able to liff. Show that the ratio of outpuolx(ua : ei-)p6,vfv wt 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 acceleratkvfi+i wd6f: 5ing by a man who is pushing back on it paral+f5:wf 6 vikidlel 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 helziv,1 .cpa 1kjicopter of mass M an acceleration of 0.10 g ujk .pc,z 1vi1apward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume the distance axis is linear andnuxq2k+ f2kbz)i1 jv. 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 Fig. 6:w a9i oxy.*ei–37. Determine the wo *ae.i:w xyi9ork 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 thr pu:-y h5vh6 hjr yl..r3fg z6swi.a*i5oxp-e $+x$ 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 oxy t m 8lts.w7nv* q+ovwef8t9:ygen 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, by what factor has its speed increased? b l-2oj -k;g1r(pmpzs+o8y1uvcmkn,$ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required tt0jc jems/yo7/l4bdb *cu 6z+o 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 traveli0 s ol9xlfimvwg q5r/4 r2 03tbl)t6usng at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average force ot ;vsevcq:ksfwh e8l+lpy 4n(o z6x93u u./7 jf 110 N on the arrow over a distance of 78 cm. What isnw (7 tsqf.ujo6 lezl/ khv4yp+;v3 :9ce8xus the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove bacsnzcd tvh(;i ftf/ *4-kward 25 cm when the ball is caught. What was the average force exerted by thz(-t4*tnf;dhics / fve ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimlgfia x.u q -+c+e,,egr)hm 4pum braking distance be increased, assuming all else is thee-,,magc gepu h4x.) +ql ir+f same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigatorcy407hi u8uw rs 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 carhuw04u r8y 7ci’s mass not matter?)    m/s

  A softball having a makmm0lxye )f 5u(hp8yl*a j7pma(36 zoss of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of azhuj)yx7* e 8a l mp5k0(( 3l6pommfayir 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 if thrown stavpwb1 w+8vy mp 13g 3ssh2r2iraight up by someone who does 80.0 J of work on itawwg vms+ypv381r 22p 1 ihsb3? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a singlr 89( uplu xgetcq)iv:8 jlk3-e cable. Dev (:x)gllrue9 uc qjt88ip- k3termine
(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 ldrn 7o/ea s*,stiffness constant, k, of 440N/m How much must this spring be stretched to store 25 J of, l *esn7rad/o potential energy?    m

  A 7.0-kg monkey swinj+n(z*ukd xdrv s*/ z6 e ng/zaw5jx+.gs from one branch to another 1.2 m higher. What is the change in potential xj+/xjew/.zk+d drsazz5*6(nnv* gu energy?    J

  By how much does the gravitational potential ene63vt m(jm)ckhq1y wnwgze0 5(rgy of a 64-kg pole vaulter change if his center ojkvg)( n53yme wq6mth(z cw10f mass rises about 4.0 m during the jump?    J

  A 1200-kg car rollinggvt5q8my 2pb2+a. ip7k-lgf9/wnhtu on a horizontal surface has speed v = 65 km/h when it strik 8n. tyqgulfg2/9+vwpb 57ma2 tkpih- es a horizontal 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 boovwr7,l yxe:s+ k from the ground so it is 2.20 m above the ground. What is the potential enerr y,x:+ sw7evlgy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevati;:ph rj u0 gh8;mvig:3aiyc(pon of 1600 m and climbs to the top of a 3300-m peak; rpmj( uph08i:g 3vg:hy; cia.
(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. )rl7 id)/pktqq,eb q5 The end of the spring is next to the 15-cm mark on the ruler. lkp5e tq)dqib q ,/)7rIf 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 marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vinaplsiegxt,xt/s. ul9)) 4b + me hanging vertically from a tall tree in the +se)9/p )slat. tlx4iug xm,b jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slidesnfz3g:+ 9wgu*scp2 ps 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 uilzls8q i 8i+2p 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 transformed into gravi7 mycnf67f+iw7 dpu:k tational potential energy w7:iyd + wf7nc6kfp m7uithout the aid of 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 .6 eb.u -uny0qgk3ataupward from the top of a platform with a speed-yguaak63 .eq.tu n b0 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 sti3ed hy:.9 ergj n,0m*ubvfwo2ffness constant is 950N/m is attached to a table andee2vy9* r30hun bfgmwjo d,:. 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 alo7qbn0a;t e*rvf+ nftv8g,5w wng the looped track shown in Fig. 6–39. If the blo qww70ft +n *vtaf r8bne;g5v,ck is to remain on the track, 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 sprioc jvot7x)+*ueqz p a7p.9 0rbng (spring stiffness constant k)p0*9urbxv77tq c . pz+ojoa)e , 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 .wt0efwx:s9 pd gl( w-whose unstretched length is 12 m, and falls a total of 9w dsp(:-etg.f lwx0w31 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 jgj ;aex 4tvgwcs+1v3/ou/ac*m ea 56:t pp9 hit is released from rest. Assuming no friction, calculate the speed at poiu5v* w;/s3x+m pvtgcjgac 1:pjae 4/hao e69t nts
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed ow +dak9 iv+s 1w-)iud-nu yta3f 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed atyb cvq a2n/+dsud xyn6* lli0k3v/ pj-l1nc79 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 pasd+6u 20ylnlv73lckbx dc 9v/sa-pnq y/jni1*sengers 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 abfnn)cy - 4j7q 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite direc , 4efh)q, s*b*rkwudntions, collide head-on and come to rest. How much r k*qhf,*4wb,)sune dthermal 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 the bottom with a spe* m3c4ttxkw; zed of 2.2m/s How much thermal energy due to friction was generated in this prkm tw3;z4c *xtocess?    J

  A ski starts from rest and slides down :j9kmf; hbed*3s qj 4ea 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 13xdm2slc.ts ylgf+sa48p(9 x 3 .0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bo m/vzs/*4wc*9 rinle5q4 okmounces back to a height of 1.5 m. sei5r4cno/*v* omkmwql9 /z4
(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 frt( y5ef*rvpi 6om rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. Whaifr6*t ev(5p yt is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 w*hxq4nkfb cw0c2dwx i;3;(t mith a speed of If the average force of friction is equal to one-fifth of its weight, with what speed wili(x*k0 342w dwhnq;;bctm cf xl it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/ idr2oj.ii 5j /+h2kpus reaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal s.t(u*d9xqiel+kh y)spring (k=180N/m) as shown in Fig. 6–40. It is noted that the blk)d9xys i h.*(+eltu qock–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 otx cw(ay9gi3r 0+ac* (a p3bzfirmly attached 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 comprao0c+3(y( ca i t3garpwxzb *9esses 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*encg6 g eucgk)x:5v o1dj*8e6( (s6hsa dpwvder” (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 lan g6:avoh*61g(5* 8(dsupc x)je esdcewkg6nv ding speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a si vht- m5gp,sx/v8j6fwxth-story windo6t5fjhw8 g/-vpm sv x,w 16.0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the ave9:nk h+mujfp; 0wt1eerage force exerted on the carpkfmn 0eew ;th19: +ju due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is thel mprz13 qgnh+j.)p3;ew( at hky)xp2 average power delivered by the engin3h3) )qezwh( 1mjplxrn y+ g2ta.pkp; e?$\approx$    hp

  (a) Show that one British horsncvymzft x3-2 b3h+l (epower$ \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 8pi/ld s::dc koften 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 sldmy/ y7iew3pnrba 4drd 8 q7+(ows down from to 65km/h in about 6.0 s on the level when it ise7drdb34 y8n ai/yp7m+qwr d( in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.l531zezm 2ub2n)a vkm 0-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 mpa q9una6)( jgotion takes 1.5 s, what average p96aj(q a) ugnpower was developed?$\approx$    W

  A pump is to lift 18.taix;er *- .uwjnx8t:0 kg of water per minute through a height of 3.60 m. What output rating (wa*jtaiw enr8;-.t x u:xtts) should the pump motor have?    W

  During a workout, the football players at State U. ran j k37 saq-lzx-up the stadium stairs in 66 s. The stairs are 140 m long anl--q3a7s xj zkd 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(u7 eo81f;ute 67i8mfdvjpki 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 (zk vy fmm.e,2gsoo7o,5i,uooutput of 120 hp. How steep a hill can it climb at a con e,2oovzm(y,i,7 5g osom.kfustant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 8/i.lbmemr7 * ujx+sizh,7 dy2 8o ina310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fricti,7 /2er7u+ iydi 88lsxjmo hi n*zam.bon is 0.45?    hp

  A bicyclist coasts down a;f*it;j+ha2x+ fhs tp 7.0 $^{\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/,;*fe 6ty1 yszwu ;9xwxipa. gh) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumpey.,uixwa* 6gsf p w;1xy9;etzr 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 of cg//dw6gn nvw2rg 2 )+g+garvf the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to filwvd g cn)2r g+n/ag+2rgvwg6/ l all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–42) in the 1936 Olympi2m .saczd: ;mdl:1q pfpz)3 uncs shows that his center of mass rose 1.1 m from launch point ts lpd cp n2azmq:f;d z31).:muo 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 se3nb6 uklkym,rr dc (02llg.o6o. :ot liding without friction along the looped track shown in Fig. 6–39 is to remain on thlbrokne,utk2(g0 lc.6d36lry o.mo:e track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping frw,vkdsnk:*irh7 j26j9qj-w ,wr m *imom an aircraft without his parachute opening. He landed in a snowbank, cr: vq,jrwj d 62mh w97nimi*, k*kjwrs-eating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of l/: htmzh9q(l+ z01r za +dybaiength L whose other end is fixed (Fig. 6–0 bqthzz9 a/yim(+radh+:zl 143).
(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 3700vlwo4j7a9 zv: -m-high mountain. The climb is made in 5.0 h starting at an elevation of 230j 7lzaw: 9o4vv0 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 wh;; z*.dr5fx8ajxp,xcp cce0hen 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 claims that itcxrd,qoq6,r 5ad u .98fntb1 is lifts can move 47,000 people per hour. If the average lift carries peoq,a5qn 6rd,fox r dut8.cb1i 9ple 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/3 j v5r3yw;zwcs and falls vertically 81 m before striking the turbine b c3 3wyzwv5;jrlades. 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 cq8 9qs 3zi9z858(lo-q pf hj ihdkgd8rircular 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 minimum needed, this answer doesn’t depend on t8khri38qzijhdz qdo(g9589f8- p sl qhe size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar directly into worr*kum qi(,j-plu a (+rk, how high coul-m lkq((*ap+r jur ,iud an 82-kg man climb a ladder 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 zvr 9(xo+hp(jat 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 saevm40:x- bkf pring inside the scale compresses 0.60 mm, and it tell0:k- m4vxbfeas you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and 6ezgo3 mx/fm .34v7ua4m2 v d,bj u+t5jabpoeswings out over a lake (Fig. 6–45). He releases the rope when hi, vvujbu z532 m4xfao/b.e m +jd4ep3mog 7t6as 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 distaybz4 ,r lwj fns usc .368v-twma2vv55nce of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feat? 8z 4 bs cjnvwm,562u 5-.ryf w3atvlvs   W

  Some electric-power comp irqmwt0;pj2*anies use water to store energy. Water is pumped by reversqjmwi*;p r20tible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. Whattj u-,j9xmc r8 0isg5h is the spring stiffh,-xumjt0c9r85i gsj ness constant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rougx2 d dexojf*t3iaa/i)m- f: -xh 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 3cmt8;u*;1,dgldg9-dkpo3oy . g/pyxaeb - ge.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume thc-pxm* uod;t kpo3bgag gdyd,e189y- g.l/;ee power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “1st1hq. *3 x0lp ds m)rzpnh9ustress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 7511lds0m)h np*q.ps9 h3u xrt z-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 vertical+ +ss lq5mbi.w1,hna zly upward a distance of 500 m, what was its velocith qsi5lna+,zwsb .+ 1my 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 f/0j o)rqo1wu,4 tzsqerom a height of 2.0 m at a rate of 95kg/s (a) If thj ot) ez1q4uq ,o/swr0is water wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s