In what ways is the word “work” as used in evew k6ii3o e2u4/:m4 dbo 8cmmzrryday language the same as that defined in physics? In what ways is it different? Give ex:4 mei rdb mzi6u8o2c4wmo/k3amples of both.

Can a centripetal force ever do work on an object? Expdl0 j9)j-l:yy x3gxnulain.

Can the normal force on an object ever do wordeiol n r+99fc3kx.7nk? Explain.

A woman swimming upstream is not moving:v;zfvc sbk*q j(2vk- with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is wo*v vcf:j v bz-kqs;2(krk done on her?

Is the work done by kini, gna5m bx9ya n7kwe+i(r /k*etic friction forces always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out from under them.b+5rai/ia(k k, g9en7* ywxnm]

Why is it tiring to push hard against a solid wall even thoughz7*rzbi ,,ls ju/ j6cy86z tldl xz99b you are doing no worklx bzzs,79 tl,lbz*9 ciu yjdr8/6zj6?

You have two springs that are iddljcp4-3tdf6 .fru . pentical except that spring l is stiffer than spring cd.j34fpf dl u r-p6t.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 constan 970o 8itpbda *ds(wngt horizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it has travele*iad7bn s8w(o t9pg0dd 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 chan7rxw7xz b/7k*ddi p5em2uvme d-o8l4ge when you jump px 87 bdlu2oer/dz57m dx*v47-mwekias high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a buildinywav)bi(rot, o8bsc rv+2/7dg, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistan2boao,ctr/vsr7w + 8d by()vi ce.

A pendulum is launched from a point that is a height h abnu*c,y g +b -1vxwdhu1ove 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 caus 1v1yu ,-*dgw hb+uncxe it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m)5f)5 baty wxa-vij(+gf/d ty rests upright on a table. If you compress the spring by pressing down with your hand and then release vy5 -i(bfa d)a+y fw)tjxt/g5it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–1jux 1pufz00 a (yzd0i33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushingay1uuxf 0z0(id1 jp0z it. Why?

What happens to the glpt(fpky;7 ; qzzc(f nfp 7;f(ravitational potential energy when water at the top of a waterfall falls to the pool bfpn(p l;fkfczpz7q ft ;(;y7 (elow?

Describe the energy transformations when a child hops around on a pogo sticktw5f7f( kln pw:)s(a nii05 ds.

Describe the energy transformations that take place when a sk r8(v,8/a8feghpgr z qier starts skiing down a hill, b/qg8 z rr,a(v hgep8f8ut after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a hiljadp -wp-e* oes rshdf*)(4j 9l of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is dj-o*f4p s- dep9ew(h)ar js*icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their pa t/b,ry3-ii jeth rather than stepping on top and jumping down on the other sideri b,3jye/i-t. Explain.

Two identical arrows, one with twi a36 p7, heulzhlz me/2bfuj jo-(z2w,ce the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow wih3(jmwf6 uz,7a2lu-,j zz/eolb 2 h epll penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simpb hm+-a:yikb0le swinging pendulum in terms of energy, (a) ignoring friction, and (b) taki:+b kaym-hi0bng friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can 5j 0 2tllhbn34yj 0pygit rebound to a height greater than its original height? Explaiytlyj2 0nb5lgh3j04 p n.

Suppose you lift a suitcase from thek4m) vw, ogch d0m,(ic floor to a table. The work you do on the suitcase depends on which of the followingmgk v(,imcd4c, woh )0: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for 9q3t.ailkdw(the power needed rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climbdm6yyl7 j(hq78bs /leuzmx *+ straight up(zy bh+*jml qlsume6d7 87 y/x?

Recall from Chapter 4, Example 4–14, op-b;*cno7ji that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pullj;n oibc 7op-*ed up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fall cp- 75r7;. gc6zwvs;yygfqycs 2.6.rypfgwq7 c syz;c7v;cy- 5g80 m?    J

  A 65.0-kg firefighter climbs a flight of stairsd r+xzv16j t nvn8j*3f 20.0 m high. How much work is requirejx6n3+v8*tfd1j vz nr d?    J

  A 1300-N crate rests on the floor. How much work is required to move fy*b 8 nxbtqb(5m,k2l0/g lagit at constant speed (a)50 btb8/ gkay( qnlmfb2,g* lx 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 9sk0 ju4h ln:/9 apjgwmovers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if jnh spgl4k:9 /j90wua the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kgwf6sy0tz:urv v 8/ e5g is accelerated by a force across a floor at a rate of for 7.0 s. Find the net s/:vr yveuft865 zwg0work done on the box.   J

  Eight books, each 4.3 cm thiclx)e)/t+ jh wnh6j6 yrk with mass 1.7 kg, lie flat on a table. How much work is required to stack them one on top of ano+6teh xhr6 )jn)l/wjy ther?    J

A lever such as that shown in Fig. 6-35 can xh j8gdc63gb2yxb)d .be used to liff objects we might not otherwise be able to liff. Show that the ratio of output force, hdbg 3c. y6 bjdgx2)8x$F_{\mathrm{O}}$, 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 acceleratin*yx/1fxvzn ;4hni2 k6 : w+tanhbyt0s g by a man who hannkw: /izf v 6ty;2ny0ht4 +s1x bx*is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter ofyxhm-i05obo+4nd(h /djad9 6t8o b wj mass M an acceleration of 0.10 g upward./ ditb 0 jo 9 b+j64n(ydwhooa85xm-dh    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 }\text{ incline? }$$(a)\text{ Ignore friction. }$    J
$$\begin{gathered} (b) \\ \text{Assume the effective coefficient of friction retarding the car is }0.25. \end{gathered}$$    J

  In Fig. 6-6a, assume the distance ax i ). ,aqkwzoj(ar(wm;is 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 xilqb-nwx (260owxf:npww54rx/a( iy axis, varies as shown in Fig. 6–37. De:r/ yw 4w5 w (nwx o6ixnqlifpa20-xb(termine 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 -bm(:ef 0inx4im5q:bggs 9 dn on a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mass odlq.g bk0 b-2lf $5.31\times {10}^{-26}$typically has a KE of about$6.12\times {10}^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled,rff9v: m0blq h)nh.j) by what factor has its speed increased? $\sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to/yeks:e.t + gx 4ew2cq stop an electron $(m=9.11\times {10}^{-31}\mathrm{kg})$ which is moving with a speed of$1.90\times {10}^6\mathbf{m}\mathbf{/}\mathbf{s}$ ? $\boxed{{\displaystyle a\times {10}^b\mathrm{J}}}$ a =    b =   

  How much work must bea;p -irlxet k i4:b.q4 done to stop a 1250-kgcar traveling at 105km/h?$\boxed{{\displaystyle a\times {10}^b\text{J}}}$ a =    b =   

  An 88-g arrow is fired fro/jmk,(xiup9tm7vu 8x zlgr 17m a bow whose string exerts an average force of 110 N on the arrovx jt1 /79u7 izkumxpr,8(gl mw over a distance 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 glog6xx/b bvx,u*y qw e7;ve backward 25 cm when the ball is caught. What was the average force exerted by v w6xx/,gb*bqux;ye7 the ball on the glove?    N

If the speed of a car is increased by 50%nv(h2uo35q5 3i wxpl 3e/pim z, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignore the driver’s reactizw( 3 5pquho 2i3 eiln5pm/vx3on time.

  At an accident scene on a level road, investigators measur:z i 3cikj; l)a3eg w)ot9(owie a car’s skid mark to be 88 m long. The accident occurred on a rainy day, (cg9jli3:t)kzi)3 e;a oiwwoand the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 ec1/e-b i*hr skg is pitched at By the time it reaches the plate, it may have slowed by 10%. Negls - rb/ee1c*hiecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 80.xts3:b 8z+mi1o0x7y;q jzz eb0 J of work b:7y+szq xi; te 3x8z b1z0omjon it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a si+v:;hsxyspl 89wmq : qngle cable shsq;+lm: vwxy:q89p. 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 muchpp6skz hj1pe ,u: v-nl-*urx: must this spring be stretched to store 25 J of potenti*-uhul s jek6z:p x-r:,nv1p pal energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. Whaez 8mcxi 80eyy, gw9e)t is the change in potential energy9,m eey0i8ge 8x)wzyc?    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter l0 )khy3z+2p.xrt ggpchange if his center of ma gr3hxy2t+ )0zpgpl k.ss rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horiefs+j8pd kch 3 :uh6d.zontal surface has speed v = 65 km/h when it strikes a horizontal coiled df hhc 63k8u+p jd.e:sspring 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 s r o0*kpfw-0mh b7;rpvo it is 2.20 m above the ground. What is the potential energy of the book relative; pkhvf r*0 prw07m-bo 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 s m31mn,yvg4w m and climbs to the top of a 3300-m peak. wm 4nmsg31,yv
(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. The end ofa6 ln(ip5 my5di/,epolj*n/ v0yc,c j the spring is next to the 15-cm mark on the ruler.,56 yn ilvmol y*a50 /ed,i/pcj(njpc 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 marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) aomas:n *kmv- x2,tz4lnd grabs a vine hanging vertically from a tall tree in the jungle. How highxk*:l 4mv- oanm2t,sz can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from restzv fgsvny3/0 q wlvba.* i9v2958(wl 7yto lvc, 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 frictionlessktbm2*h v3jk0i: -bke ;mj)gi 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 i-7bpgl 4+opl is transformed into gravitational potential energy without the aid of a pole. With what minimum sp4b- ol7pl gp+ieed 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 witt(9s -5hqdx-luc+meth a speed htsx +tqe5-c9d(u l- mof 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

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

  A vertical spring (ignore its mass), whose spring stiffness constant is 9jiijku:(rl hi0-1/r ofr ve4050N/m is attacv0o (4r/1rkj0: lfijur-hieihed to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown in Fit / c1dlv*9ugbg j9hx-g. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h jbhu9lc vx gtg*9/-d1 must it be released?    r

A block of mass m is attached to the end of a sprhddso z- rc1tm tnq32r9*z* r7ing (spring stiffness constant k), Fig. 6–40. Th3* 7m- 2 z*1cqr9onr dtsdzrthe 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 tiu+;t9f s yt+4yxunk2ded to a bungee cord whose unstretched lengthd t 2ksux4y+;t+9 ynfu 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. z2cr6eft1 gj+k st5u /6–41 is dragged up to point 1 where it is released from rest. Assumgeuj /zcst5r261+tk f ing 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 speer 54josfpny( 1d of 12 m/s at an angle of 33 ${}^{\circ }$. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an elevator ce/.wys,gi2r ohqv). 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 ) .shcr/,w2 yqvg.eoipassengers 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 qdg pe m50n09o4llu- v7.8 ${}^{\circ }$ 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 0g+exf 8j)lv edirections, collide head-on and come to rest. How much thermal energy0 e xl)eg8jf+v is produced in this collision? $a\times {10}^b$ J a =    b =   

  A 21.7-kg child descends a slide 33 k3l3giesh* tos:fm 8(pxwx: .5 m high and reaches the bottom with a speed of 2.2m/s How much therh3tw8( :ss3gp meki*oxf: 3x lmal energy due to friction was generated in this process?    J

  A ski starts from rest andwbq v f,d3u-atg*s ) cinub5*, slides down a 22 ${}^{\circ }$ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the p02dl-gs q+wv byn3t,lj yx(4 ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of ff 7pos/av/ 8k1.5 mo8fv7fk /ps/a.
(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 fr;n1xet3 t alv)fl :chcgm(x/ 1om rest, is pulled across a floor with a constant horizontal force of 350 N. For the firstclgh/e :m1 t1)( fxvc3 x;lnat 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 m/g 1q6m dr m-1bbr nqhgo7d56point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed wilmd 5-od1r/ggq6n6 mbr 71b hqml it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reacokj7g( wyhd *a8coby5p;(r19 sykb 4lhes 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 att p ywnvc w4cm4.d:l15eached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equimw5y1 c4cvn 4d ep:l.wlibrium 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 firmlci ;wm3.a za; ts;dwt;y 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 compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium pos3.;t zimt;s dc;w;a waition will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 98vm.ei9n)8 1vdncni zw5yb ;/p 0 kg including pilot) that was launched horizontally at 500km/h from a hep)8/nmc iin1 ;w5dvzy9 bve .night of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 ${}^{\circ }$ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a uavg.u29q .popus0c4 v+7cgb/ll : kt315-kg piano to a sixth-story window 16.0 q+tpv:sb7vc.g2 l a g 4u.9/cpuoklu0m above?    s

  If a car generates 18 hp when traveling at a steadc*vh-k gnogd1qx m9-9y 88km/h what must be the average force exerted on the car due to friction and air resisth-*v9g xno1q9 kcg -dmance?    N

  A 1400-kg sports car aqe9.hax 47c hrccelerates from rest to 95km/h in 7.4 s. What is the averaqh9r4xa .ch 7ege power delivered by the engine?$\approx$    hp

  (a) Show that one Britisz+i2s7 zzdbk e7i wfm8f)x5k;f bap)2h horsepower$\mathrm{ft}\cdot \mathrm{lb}/\mathrm{s}$ 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 /(8ar6c:bi 2zemblhz “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times {10}^6$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?$a\times {10}^b$ 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 thate6i-y9*m 6pv v9nw8vgljiki * her 1150-kg car slows down from to 65km/h in about 6.0 s on the level when it ilv ym ni*gkwiv68 -9 pj9*ve6is 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 3.0-hp motor at* t*v. odyi3xov30zds ou:c6 /s9ao do in 1.0 h? $a\times {10}^b$ J a =    b =   

  A shot-putter accelerates ahlwr+- i;d dj-d4 ,ir 3nwrn.t 7.3-kg shot from rest to 14m/s If this motion takes 1.5 s, wh+id.43n ddt-;,ww jr- lnrihr at average power was developed?$\approx$    W

  A pump is to lift 18.0 k; *h x u*d,l uk+7t0wahqng1wdg of water per minute through a height of 3.60 m. What output rating (watts) should the pumpq1 wntwkhda* *uux7gd, +;hl0 motor have?    W

  During a workout, the football players at State U. ran up the stadium staix*9ab)tkjhg )rs in 66 s. The stairs are 140 m long and inclined at an angle of a9bh j gk)x*)t32 ${}^{\circ }$. 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 cycld: k1k-av ac0uist 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 mr 6cv 9nythjd,a3:5 saaximum power output of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional force na ,j:a5 tdh6s3rycv9s add up to 650 N?    ${}^{\circ }$

  What minimum horsepowe7wj,o.te k(cghxi7r8 *6gh3lgrat8 gr must a motor have to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient ofre( 3tg 7.th8hao xcgk6 ,l7 ggji*w8r friction is 0.45?    hp

  A bicyclist coasts down a 7.0 f+)xh-y4abb/6)cd xljfg k3w ${}^{\circ }$ 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 designed t: s 69k dq.z,giq)wnxto 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 cargkizwds)n. tx,9q q6: has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times {10}^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the grounnez ,f0gsh76 omg*q ocow;; .pd, 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 rs;qe pono cw.706, fgmh go;*zequired 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. 6–42) in torcak3lnvaxq8 / s 4d1z( wqd*s7h0l0 he 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 trave ad0s10hsxoaq( 34lkzc7 w8*lv/rnq dling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track eio t:*b9ad3 5 b:mzmzshown in Fig. 6–39 is to remain9bm i:zz*:3tb m5d eoa on the 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 fec m0e+ol5qr:j3 av r:hll 370 m after jumping from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, b r5m3+lqjhvo a:e:rc0ut 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 length L whose otnrv9fy ayao*( i,3+qlher end is fixed (Fig.yiqrv(a9an +ol,yf* 3 6–43).
(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 iwd *x-(u -hj5qmjgm)a 3700-m-high mountain. The climb is made in 5.0 h starting at*-5qjghx) md i-jumw( 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 above a hugex8x/+fyixuj5 y+.ppp spring ($k=2.2\times {10}^5\mathrm{N}/\mathrm{m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts ca,fn)dp ex7a(m f4p4we w6yn s8n move 47,000 people per hour. If the average sm8e)apy4( e dwpxfnf7,4w6 nlift carries people about 200 m (vertically) higher, estimate the power needed.$a\times {10}^b$ W a =    b =   

  Water flows over a dam at the ratelf0)*b i735v lg:fsc6twrg+oa0ty tm of 650kg/s and falls vertically 81 m before striking the tu:cr*y53at 6)w0l li f ts 0ogg+ftmbv7rbine 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 circular vertica4 xowaf;ygx v (ul8cc8hk0gar 4nb-)7l loop (Fig. 6–44), the difference in your apparent weight8h(8v0;xfwr) blg 4cugok yca7 a x4-n 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 the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candy bar dy k fy,94h68 vloh1vdsudt,4oirectly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (6d,dokf91 v t uysvl,h84h4yo=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 ,8hh ,n qcqm9hidi /b6of 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 inside the scale 2v2x.r+e,ovua lpixj fv+;y1l) khho ;sku 01compresses 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, whalxvx.ok)vy ve+h0212u h 1aps; kur ;fjoil,+t does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swin:k0v tcr ( / eqdo8ak2-il(jsbgs out over a lake (Fig. 6–45). He releases the r /ec(rbvitao2lqj- : (0 k8skdope 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 at hze27c) , s8 adbyxujexig(q7:q:qr.hlete climbs a vertical distance of 5.0 m in 9.0 s. What minimum power output was used toqiqjaexgbe( s x8 uqr.:cy)727,d h:z accomplish this feat?    W

  Some electric-power companies use watefn7y+ 8 cndkw2n n/vo 4j1b:ecr)ki;xgd )q-j r to store energy. Water is pumped by reversible turbine pumps from a lon:d)j)/j8f c4;yq xrbko 2vwec n17ink-+g d nw to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times {10}^6$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 cuup,uu um7so yr8a obj/7.; fdr4-t ddk* 5txv5t in half. What is the spring stiffness constany,djub;f5s*u 7kvrdttp/4o 58od.um -xr u7 at for each of the two resulting springs?   k