In what ways is the word “work” as used i 6dk o -0ndkej7u6a-bdn everyday language the same as that defined in physics? In what ways is it different? Give e06d7d kjoke -6 un-abdxamples of both.

Can a centripetal forceo*2 rz.z+qms;;pzmd+ 8 lese m ever do work on an object? Explain.

Can the normal force on an object ever do work? Ex 4w5qevyqh -7rk 65fsccp0 1stplain.

A woman swimming upstream is not moving with restz hg:*a*tohxd:1 0sipect to the shore. Is she doing any wo0z*1hi: g*h odtsax: trk? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces alwaysmk0bu-+t , ;plg*p jda negative? [Hint: Consider what happens to the k-lpp0a*mj;,+dg ubt dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against azr/qy 4(n0cfw solid wall even though you are doing no work?(4c/y fz rq0wn

You have two springs that ng/jsuvp0 x(h+gp*5b are identical except that spring l is stiffer than sprg(p5jpg+ x/ns b vuh*0ing 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 horxyg0ufb)hkg ; )lj2q dbd/7,rizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block starts f)djd0 /b;r, gbhlk )ufy qxg72rom rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does youro7k);usffqf q;y4i 2csz (7 ln gravitational potential energy change when you jump as high af2 q7inszyl 4u7;;fqco()fkss you can?

In Fig. 6–31, water balloons are tossed fro e5lgsak 3w0q yv-)q/pm the roof of a building, all with the same spegyq-lek)/ vq3s5p w0aed 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 heightq4+zxwf+zwovnt a2j 1pwp/hs (39( tc h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is diret1 woqvhxsw2+jt pz3f /wpz(c(9na4+cted 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 comprec.k2k9:l(x 5 qirvz9kvl wf1fss the spring by press 9ic fzxk(f :v.5r l2wqkk91vling down with your hand and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a stee rwvv356 ygsli3n3 l /s-ri6uvl wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoiv3 w5rs 3vriu-6i6 vsl/nl3gyd injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top o55qa 9olcqkl65/ dr :zv:auc kf a waterfall falls to the pool bela c:dqk5q5:lzo5v/r ak cu96low?

Describe the energy transfor w4t bhg:9xv2gmations when a child hops around on a pogo stick.

Describe the energy transformations that take p2nnw1 /1zjmorlace when a skier starts skiing down a hill, but after a time is brought to r2m1/jn ornzw 1est by striking a snowdrift.

A child on a sled (tvvzziwfiw b 6+6p() rwmsd 20.otal mass m) starts from rest at the top of a hill of height h and (dzwp)6mbw0fri i.s+w6zv2v slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rx 4xb1oc hyr*o (trfxk6b*t)lx ;3ow /ather than stepping on top and jumping down on the othex 1lhrtb4 xc/bot 3ry w;xo*(*fo)k 6xr side. Explain.

Two identical arrows, one with twice the speedhw*t mm;9)nlf of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will phfl; 9nmtmw)*enetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) igno;9sw lb9r (pugbwpgbhkw3 e 7 3*x96il7kj,gwring friction, and (b) takikkh3 ge,7 wuxwg7g w*b963bbpslrl pw j 9(;9ing friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it re-wb5fppcfsk.tt 6 7sd1qap7(hz5 e/zbound to a height greater than its original heipw-b/ 5p tzpzf .c7dh (s eqkt6f175saght? Explain.

Suppose you lift a suitcase from the fl5.qvnp7 +rdq+qgee*t.bvi -+x-7ol4fdz divoor to a table. 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 time77tdvv +fo+qp - dbevg+.iidr qx 54.-enqz*l it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power needed rather than theyn)u/k cok4 x)gq0,vs work.

Why is it easier to climb a mountain via a zigzag trail than v9 vxbc8 / ai.t3sa6lwto climb straight ut/6l3sviw.v8cx 9 aabp?

Recall from Chapter 4,wvy03wylf 8vkza 447p Example 4–14, that you can use a pulley and ropes to decrease the force needed to raise a heavy load (see Fiyw z ya44klf7p8w0vv 3g. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg s 7mf,i ;wuh+cb) wvz5pile driver falls 2. fwviwum+,hs5; b )z7c80 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m high. How mb8lhhvn3mka*n(4 r d (uch work is requiredhdv4alb(38 n(rh mkn*?    J

  A 1300-N crate rests on the floor. How much work is requiredy0*1w61* y6qaqii uremp ot1 n to move it at constant speed (a) 4.0 m along the floo1i0 r1n*ta6eqp umow6 *1i qyyr against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a7a gfqn7j7 wn7x)f 2j yq9os;s5urks , 160-kg crate 10.3 m acros7r29us5safns,)gnyox f;jj k q77wq 7s a rough floor without acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acrossg vhv:9f9/j5 cjar 7fcdd*dssb9k6;b a floor at a rate of for 7.0 s. Find the net ; /ds v99rjb asdcb97cd:hvgkj6 f*f5 work done on the box.   J

  Eight books, each 4.3 cm thick with mass d 1nac6j44jxnsj l u8h.e8h t01.7 kg, lie flat on a table. How much work is required to stack them htjh ln84dej6jn8.s 4cxu10a one on top of another?    J

A lever such as that shown in Fig. 6-35 c;;v;rt-:1a.le wd p k1)ck m l0nbl ljsml*(gqan be used to liff objects we might not otherwise be agd; (v -p cb1rwm 0llsl;qkka)1*l:.lm j;tne ble 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 i bevo)15w*ora o-:f2:pqm kw3.6 m down a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient ofmqk:faor p v1*-) ow2wio e:b5 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 n+l3hmxv s3j6n r+d5 ha helicopter of mass M an acceleration of 0.hm+hvdx+65r 3nln3sj 10 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

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

  In Fig. 6-6a, assume b+ 8fbmlj;5 6dcb a:qfthe distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varie5u bb x7+7iyeis as shown in Fig. 6–37. Determine the work done byu +77 yi5beibx 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 partic2km, ucxy 5/sov j+ mo,x*6ijjle 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 oxy pi.q :f ye,1463js3dceh tfvilc2 p(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, bzert:b,upfb q f)8r,c+ (6ik o;(zqoly 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 req*9.z gc9 : 6*p;znfr ifyihiwuuired 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 styq7vq b92b/ez g02zix op a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string ev2sf*2ugtdxrn 3 h*,zpvyc6f) v (cn:xerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leavef,2pgvy (:) 6n*z*v u3vcrxcs2n tfhd s the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm whenpk2 meq.n q0202y v zqyqhd6)h the ball is caught. What was the average force q2. qkdmhq0)e0n 6 q2zy phy2vexerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what facra)(uy yhviv-2()l0vylz yw6tor will its minimum braking distance be increased, assuming al)vy w)yuyvlra(2zvl6- 0 y(h il else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a cari *1* kktewrl1 qk9mt4)fpd5d’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 detetl*dfpmkq*e r k41d 1 )9k5twirmine 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 0.2c a4et6p+9sr(zzms8)t vu uj,jlc *n55 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estu zj enr a),4lsjtm c*5t6+ uzs(c89pvimate 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 straigljr)qmgy zf-e2,90kh ht up by someone who does 80.0 J of work on it? Nl,qgr 9 jey 0-m2kzfh)eglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acce 1 k0yhd84)pszzd:puk ;n 6mreleration by a single cable. De: 6d1krh)mdpzk 84n;p zye0sutermine
(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 c7 3wyp 6thss*eonstant, k, of 440N/m How much must this spring be stretchewy6s7tep3hs * d to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch tr4re d18m9vsz1)pznxem/ n r *o another 1.2 m higher. What is the change in potential ensd)mnx* 9/r zv1e8rm1e4 nzrp ergy?    J

  By how much does the gravitational potential energy ock/d6ea 34vvtp(,,cl z o lkpd+ewv3,f a 64-kg pole vaulter change if his center dvv6 4(ol pac,zd k+33et,v ,c/wkepl of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rollin:xo4tyvv6jfad)zc 8 y2; ja. cg on a horizontal 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 is the spring stiffness constant of the spring? ;y .cj6vajfa4vt:2y zo xc d)8   N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2.20 m arhxvz*6o7 ahs q4uw- 6eq /,eybove the ground. What is the potential energy of the xewhaqzh6yor* v4 q /s,67eu- 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 a ng7j3if s;4 mfmjac0*n elevation of 1600 m and climbs to the top of a 3300-m peak. i;gn*j04jm73amcf s f
(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. Thei uc*,/sd kdab -:6xu-c-iduzy5e t t1 hsq56a 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, whesde ky5u-zi qa-cts tx a1:d5 u/*,hb6u6cd-ire will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3v30*zy*j qf85zqy(7jpef pji m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swingji8*z70 fpyfv y*jqj3ze (qp5 upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting fr 3h 4obe)to0 (jab23vosj7x grom rest, 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 frictio03b -u vsf.min, j7qqhnless 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 enemlnt 701vck)b :d -c12cyvvd brgy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order tky dnm ) 1l v:vbcb0vcd2c-17to 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 th0 8wje,tpn*n ,3oax 2rpo1nt se top of a platform with a speed of 5.0 m/s3w psj0er ,ot,2n*tnaxn o1 8p. ($\alpha)$ 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 7b /od6n dybn0bq/9t)gjs /j scf q*z6is attachedyjbq/tnj7 f ) 9bb/nos0*dgc/q 6 z6sd 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 loopejxpfg 8. f0 6ach:ee vdjrx g6vg,,,jkp. 5vp0d track shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minimum height h must it be a60 . hec,:0g,xjevjfgpv. pd,fp5v 8 xgjkr 6released?    r

A block of mass m is asphb z .o4oi50 l6xsf1ttached to the end of a spring (spring stiffness constant k), Fig. 6–40.s6xhoz 45 lfop0ib.1 s 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 brim tup/6hy)vd 8dge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculatv pm/tu h)dy86e 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 t+a/j+ oz5m3impo rk +lr 9k7huo point 1 where it is released from rest. Assuming no friction, calculate the speed at pok5mur3 phl9a/ 7+koo zrj+m+iints
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at t5:si/uab lg:)uve,ua az 8,xan 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 plac6 uz:2hdj76/ oonvcoxed at the bottom of an elevator shaft. If the elevator cable shouz/ o6 62oju:dxn7 covhld break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers 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 tox+f u s64fy0ok cycle up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in ovledoro. teq6j 9svblc31.9 1pposite directions, collide head-on and come to rest. How much thermal enerl ..9v3ldroqovtbeecj1s 619gy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high a3lk p,c)tz xlo0.b/if nd reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was genera)ix/.pzfk l 03colb,t ted in this process?    J

  A ski starts from restub mj (94ttf+4xb. zgt and 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 fro4j mjl/dhce3/ 1ma. givzm:/cm a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a heigrg9-ay/. r:kz 9 /rhelfce6 rpht of 1.5 m.:peyg/e/crhrz l- 9rr69k. fa
(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, starti9l6 l l1qp7welng from rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, lel691qp 7lwl 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 cp-h2bh hl12v;xs ann;oaster in Fig. 6–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its we1 bs;xl-;nhvn 22aphhight, 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 stead6sx6lj40f.rkbo nr t 4y upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring fs:6ug 9em6) vyixbw*(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 equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between ty)ie mv:g 9fb6xsu 6*whe block and the table?   

  A 280-g wood block is firmly attached to a very lighewtx1sou/aw4h q7+ p,t horizontal spring, Fig. 6–40. The block can slide along a table where the coeff4 + /x auw1sewhqtp7o,icient 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 spacen71tgao v:rq / shuttle used a “glider” (mass of 980 kg including:/q gr an7ot1v 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 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 31xdwwmc 0x6u7 -5-kg piano to a sixth-story window 16.w0dx-6xuc 7wm 0 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the aver .,qvjjw6siw/q8 s-xd bhp q28age force exert68sj wq8pbd/jq w ,iv2x.-shqed on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whjdo xwd,v 0elfs1 496zat is the average power delivereoj w9dz 1l6,fsvex04dd by the engine?$\approx$    hp

  (a) Show that one British hor yyx5vv(2r 0oa0n n/disepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kilowat5uuozx.hze,4nh 3 rfm:f 4i9a t-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-yjxxn)6vz bemsj- * * 65km/h in about 6.0 s on the level when it is in neutrav my* jz) e--xjbxns6*l. 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.(-qy eql)ozk50cl, do3u kye+ 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 q2yiw x3r (.rgthis motion takes 1.5 s, what av qg3.( ywrrx2ierage power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m. What 3myexg 4hc)m5 output rating (watts) should the p43x h5g )emcmyump motor have?    W

  During a workout, the foow+t)r+ yey t8mtball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 mrt tem+)+yy8 w 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 cyclistkdts2:vmr89 d j52hor climb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. How gu0pvd.*bwk1bh 8fv vsh31:lsteep a hill can it climb av10sgd* bh1fkb: pulv.wvh3 8t a constant 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 dlk2e2v/s u/w irag a 310-kg box along a level floor as2v e2k iwu//lt a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts dosps//z*5+zsc3g kj gswn a 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(t lh;9fnw.lq rquicn*s -(6p/8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers 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, ni(qw;l/*.s 9 hun -t6rpclfq 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 off thkqtmhbl 3,ghf, +j2b.e 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, 3,b.lmfjhqh2tbk, g + and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famous long jump (Fig. 6–4;p qv2ida -n6s7 prkx)2) in the 1936 Olympics shows that his center ofp-2xvirnkqs7) d;a p6 mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding +9e +w;hjw+ bc su -(gcsq yjuon*a(,vwithout friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very t(b ssch- q+uvjw(*u g an+jw;9yc,o e+op 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 from an aircraft without ho /t-y0r0lsofc ;2 uxqis 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 tey l;u0c 2r0-tof qos/xrminal 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 other en)f9zx h(y th2is ;bo-ad is fixed (Fig. 6– zhht9-)(yxb;i2sof a43).
(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 mountain.ch:by (w c1b9l The climb is made in 5.0 h starting at an el1c bcbh9:(lwy evation 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 elf t62 dw/+(sf+l j60msqkkmon evator 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 its lifts cav*/xoh r.h8yx n move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estihxhv*/y8r . oxmate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s anup+xn35i b d.drqtt20d falls vertically 81 m before strin3 tu tqdibp.2+dr0x 5king the turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a ci5c7t sauw r u ae4m +hqw toh.tx+1.4)ca1fq8krcular vertical loop (Fig. 6–44), the diffe ws.aqf.hr1+kw 4 8ae +chqtt5c auuo7x1 )4tmrence 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 the size of the loop or how fast you go through it.    mg

  (a) If the human body could 30alh ccx +po*jo6k ,jconvert a candy bar directly into work, how high could an 82-kg man cl6*a ojc, cl3hjkx0+o pimb 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 at az6 u ra6js*+uvn upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compressedm f2v3x b0/mls 0.60 mm, and it tells you your weight is 710 N. Now if f3v02b/ldmmx 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 swings out q* *o 5nn,*juiva*k fxover a lake (Fig. 6–45). He releases the rope wqvijo*nk5a fx* ,u*n *hen his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climb6l) 3mu6kbtg4wx2hzqal q 3 4es a vertical distance of 5.0 m in 9.0 s. What minimum power output was used to accotehk uqz3g6 xa)3w q6 l4b2m4lmplish this feat?    W

  Some electric-power companies use watew6-* n.owunez1tx1 wpr to store energy. Water is pumped by reversible turbine p 1 p-nzw1e6nutw x*w.oumps 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 halz9i0 .c zv*ovla dm90rf. What is the spring stiffness constant for each of the t0mco9zval i 9*.zv0 rdwo resulting springs?   k

  A 6.0-kg block is pushed 8.0 -0fozy s8eno+m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how long will ir2h 64*n 6xc +ms(aoot*fzkrdt take to accelerate(z6rf+**r cx oomthns2k4a6d from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the j/cobtjl/z.2( dmt (kpatient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the tret/b(d(mzcj2j/ l t .koadmill 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 50.1ejb l,tyy .qf8 syzj-km;fn5ix.h10-kg rock vertically upward a distance of 500 m, what was its velocity w.mh.1- ;zbiy 5, 8kq1sftey njlfxj.y hen 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 height of 2.0 m at a rate of 95kg/ahc8o.jbwfgx+) fh82 s (a) If this water wheel is set up to provi 2 hg ha)8wcf8bx.+fjode electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s