In what ways is the word “work” as used in everyday languc ,s ik5zfh2g:age the same as that defined in physics? In what fc,5 2z:h kigsways is it different? Give examples of both.

Can a centripetal force ever do workem9zxft6 6v+y)b- khk on an object? Explain.

Can the normal force on an object ever do work g op(;-owrp6q? Explain.

A woman swimming upstream is not moving wit +.rsw; r(q:fvtkyo5,1m ,v(i kli culh respect to the shore. Is she doing any work? ,ciy :(iv5r(l um.vk;1+tl kwof ,sqr If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider f,w 2asvxzp 42what happenssxw2f z ,24avp to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wae rk5q og) n9h8l)ca ;8m3 clc/osso9pll even though you are doing no work?99qlg)nl c)me8 ok s3pr/coh a;8 sc5o

You have two springs that are idencj(e(; x.kfux+ vuqd+ tical except that spring l is stiffer than spring 2efx uxd (c+kq;.(u+v j $(k_1>k_2).$ 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 blockcvn*vt6+ ldp 0 that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by v0*t6pn+cv dlthe 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 yozjn4 y1ya:/pjur gravitational potential energy change when you jump ajyp4/1ayn:z j s high as you can?

In Fig. 6–31, water balloons are tos,v.cursz l r,/sed from the roof of a building, all with the same speed but with different launch angles.zv .,u,rs/rcl Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above iv.b,w5gp fh( rts 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 cause it to swing the largest angle from the equilibvbgw frph5, .(rium position? Explain.

A coil spring of mass m rests upright on a table. If you compresssj-a6 os1acv6 the spring by pressinga6ac 6o-j vss1 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 hungrey5w01vsmn46ll x(s from the ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall withl ssnrwyx156em(04 vl the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential e8r:r05dwo gu 7t n:fgmnergy when water at the top of a waterfall falls to the pooltu dw :rmg5rf no7g0:8 below?

Describe the energy transformations when a child hops around on a pogo stick.w1p w5(o1wl ivk;z7g j3j2jfp

Describe the energy transformations thc ilq8+b / wv2j* wtya+fr34rhat take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdri+h*qrjcl w8f+i wv/ y24rtab 3ft.

A child on a sled (total mass m) starts from rest at the top of a hill of heightop+u5fs3tv mn-xu (3 .jin-i o h and 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 sn-3(5ujinm o 3x.p-iut o+vsfn ow)?

Seasoned hikers prefer to step over a fallen lpn.esec,s *u5 og in their path rather than stepping on top and jumping down onp.sne c,ues* 5 the other side. Explain.

Two identical arrows, one with twice the speed ofkvcixz -x xg;4ajg)o/ a*m +a9 the other, are fired into a bale oai)vx-xxa/aog z4cg j+m *; 9kf hay. Assuming the hay exerts a constant frictional force 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 enrl nm et-3/*nlergy, (a) ignoring friction, and (b) taking friction into account. Explain r lm*lte-n/3nwhy a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greatm+ e r/fi7 .lk9r.uaater than its original hei .fula7reta 9. km+/irght? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on the fh7e:a.n8- oyb4yiu.o 7*wtu8h sdv hsuitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) ttbh .8: ey-vo7s8 afiuy*o .4und7whhhe weight of the suitcase?

Repeat Question 22 for the power needed rather than the worpn.5fj )7gwg jk.

Why is it easier to climb a mountain via a zigzag trailwut , lslbj:yz 7av5.l:4mp.w than to climb straight up j: mua.tb. 54ws:pl7yvzl w,l?

Recall from Chapter 4, Example 4–14, that you can use ajmv mo) xl)9b8rhjb-4 pulley and ropes to decrease the force needed to raise a heavy load (see Fig. v9b )xmojj )bl-4r8mh6–34). 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 w 656i5vezvb i+sjbc)chen a 265-kg pile driver falls 2.80 mi)vc5 e+6cvbijs b5z6?    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 m higl09 khr9h o*m:cn/ ybtkf 702w cepc+ah. How much work is re* /9h0m0nf bw pc+y9rh:cl 7kt2o kecaquired?    J

  A 1300-N crate rests i0wbcph) jh(-on the floor. How much work is required to move it at constant speed (a) 4.0 m along the floor against a friction force of 230 wp(hj-0)b ihcN,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizont9b ,pcv -u8csjally) pushing a 160-kg crate 10.3 m across a rough floor without accelerationc8u,sb 9 -cjvp, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kgw(c eentdt*k ;ab/poo 7 zvak6rf1; /hw-f h-. is accelerated by a force across a floor at a rate of for 7.wva-o .pt6h de(/h; nkaw7cof/f t-e bk z;r*10 s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, li/eo31 tv aw.ole flat on a table. How much wor1ow3tv/ oel a.k is required to stack them one on top of another?    J

A lever such as that shown in Fig. 6-35 can be used tru jxg(63 f.z xr62mkbo liff objects we might not otherwise be able to liff. Show fzrg x.( x2u6k6mrj b3that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down..j. /;r6kka usiprjd 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 of kinetic friction is 0.40. Calculate: a uipk ;./6. jrjr.ksd
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an ach.x xnr hb+f,(celeration of 0.10 g xh(b.nf ,h+rx 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 the distance axis is linear zs58yoeyt1s ) 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 al1kldtn8p0h ivb6 g :(song the x axis, varies as shown in Fig. 6–37. Determine the :l(g68 bt0khnivds p1 work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a park hfwb5m 7rye t:gu;1/ticle 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 oxygeht+1;qb4 emavn 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 u;9nxfi;m mwoo44m)m, 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 stop an qln 6u7+ k(fqu6pmy6n electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-kgcar traveling at 105km4z u xjd1x ft3z)i09tg/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).(cc3h,a :, p 6upyenhtn uqf 110 N on the arrow over a distance of 78 cm. What is the speed of then :tp,cy3hqtp,6u( cn)a. euh arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s nh /(m,njb+xqyda 4cgo1n-n3 glove backward 25 cm when the ball is caught. What was the average force exerx nd3o,+4(b/ nhn nygq m1j-acted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor w5t 6z x9 lvfs:.:pi he7fp7sboill its minimum braking distance be increased, assuming all else is t .lishz6xv :t5fp:bpes9 77fohe same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid 02hvm /xkp;- rnaeh )dmark 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 ()2m/px; rvhkeh0a-nd and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at/khq0m5 l8(a 6sijce q(gjtnv9a.uq. By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if thsq5a9jn6mqj 80gv uqikcte.(/ lh .a(e 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 802 fkeew eqk2..77 edpq*wwl,e.0 Jew2 q. 7 2pkqle.7f *w,eeedwk of work on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an r5vv qgp10n3h acceleration by a single cable. Determi3 5pqr1vn vg0hne
(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 st+j: bh02aqe 6jf4lagz iffness constant, k, of 440N/m How much must this spring be stretched to store 25 J ofb4+:2gafjaqelz 0h 6j potential energy?    m

  A 7.0-kg monkey swings from one branch tph78b trmm6809 q)a)zt dp-jju.pm0l 2jurvk o another 1.2 m higher. What is the change in potential energy? j.z2 u-a9l0 rt k drjmp78pb)t0uvhq6)mj mp8    J

  By how much does the gravitational potential energy of a 64-kg pk mv b.0o1wo6hole vaulter change if his center of masshb m6ovo .k01w rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speaqr )uzf3c jm49ob:z9 ed v = 65 km/h when it strikes a horizontal coiled spring and is brought toru zzo3m9qf4j 9):bca rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is 2) fg0qmev)34-zd uwir.20 m above the ground. What is the potential energi0-43qum d fv))zegrw y 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 elevation of 1600 m and cn 0pj0 7isw9oclimbs to the top of a 3300-m pso wi 070cj9npeak.
(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 enj t6;-l9lap wcd of the spring is next to the 15-cm mark on the ruler. If a 2.5-wt6j;l- cpla9 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/6k7t34 vt4h or+c wdwc9xk. jks) and grabs a vine hanging vej+6374c . owcr ktdkkxw9hv4trtically from a tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a fril0k,cbh1 qcw,b0 gzv0ctionless 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 give6zhoih 2oo *f),ylt)kn a shove up 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 gp 7yt cjnn + dmxjw8s1j760.1udx)xfcravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her cent7d71 x .xmt1jf)sudjy08j n6 +pcnxw cer 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 platbxby. 6 a iso)sbxzqc8;1.nk+i9ezt- form with a speed of 5.0 qzsnzksxa.boy6 ib.tb9e-+8x; 1)i c 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 (ignorep .e6do1d pwq) its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to . eq)wp6d 1pdoa 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 5s ag9fg+ql1 ) ma*etmshown in Fig. 6–39. If the block is to remain on the track, even at the top of the c ae )*g9lt5 afmg1+sqmircle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spr8f9 ykfkpyyb 0r p(83ping stiffness constant k), Fig. 6–40. The block p(rfpby py8yf 3 89k0kis 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 j53r/p*)*tzkf+ip 0bxz jt xw le1g:ea bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 mfi zk3:/e*j) xj5wpb lrpz+t1t x0e* g. (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 drag,hzu/4 xceto ,ged up to point 1 where it is released from rest. Assuming no friction, calct/ux 4cz, he,oulate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of rg4,hx )dnybf0q .pisd 1k0+m12 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 s i-zz(-37qp.v: splqhblc rn+haft. 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 passengers undergs +li-( :7nvpr - zlcqpbz.h3qo 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 7l+ mh3fbgdfdh((uz,zk i;7:p.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 2 c;mf0( n/urfuivbh9 kg and traveling 95km/h in opposite directions, collide head-on and u /f(0 mnvrc2 9uif;bhcome to rest. How much thermal 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 62pdbf9o mns(/t wrxfl-(z*kz1 s f c9with a speed of 2.2m/s Hopst 1mko9sbc * f29(xzz6r-ff(ln w/dw much thermal energy due to friction was generated in this process?    J

  A ski starts from rest zu..pcbh) bzp1; 3q(awlo)r j 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 from a tree 13.0 m above t4xvq6g :m-xq/zo :dz wqx -y5the 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, anm(aed 49wzb5qn8mj6 27c zep4brh pom:,qj 5ad it bounces back to a height of 1.5 m. abrj 64497 z cw:nee5bp5 qpjoz m,q(dma8 mh2
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from reyic 4wkj/27bl3m z; most, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and fb4k/lioj y ;c27 zwmm3or 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. 6a 01b1czklcx00* 9kzkf r+cex–41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance t0fz1 cc+x 10xkaeb0 k9r*zkclraveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/f+ ds( yh1eip7s 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 sprinkbfhen)15 :-fw6 hc)3hwln s tg (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 b c)ftl:bns h)he-nwh3 5w6f k1eyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig. 6r;lhw+ kp2sik 4k /uy2–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its firss4w/ kilkrpu ;k2+ yh2t swing?    m

  Early test flights for the space shuttle used a “glider” (mass of 980 oipiog1 . 8k goixs,t8g7b a8-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 (aosi8o,-i8gxkg o. b1pt78a i g) 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 tl z)q*vh2anbvsb u 0,;o lift a 315-kg piano to a sixth-story window 16.0 m abovn,)hu;bb2va*lv qzs0e?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the kgqv-1e,o w6m average force exerted on the6ve -kg1m, woq car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. Whati hx9j /3xqw8zqbn,ema)ce7 * is the average power deli q e8xhin9/mej3,7xcq )*zbawvered by the engine?$\approx$    hp

  (a) Show that one Briti zao g-m;ike .(16bbsvsh horsepower$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed in the form of “kil tp;n,hkcu1g-owatt-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 slows6foak-t4r fd; down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what4ka- ordft ;6f 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 morye o:10s3mpotor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from resf+x jdqub0+ n-ho/wrt:ils m-e():myt to 14m/s If this motion takes 1.5 s, what average power was dev0msqrfx wjom/- ) e::u+yb(l-itnhd+eloped?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a hev 7uhcv16o9s(t9 buc xight of 3.60 m. What output rating (watts) should the pump motorhu1ucscb7t9( 9 x6vov have?    W

  During a workout, the football players at State U. ran up the stadiu8*hj;6:md3xxst rt .yf5l6 k vpy4pyam stairs in 66 s. The stairs are 140 m6pyxvpsh.f trmx6y 4 :d83*y jl5kat; long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist clim48rbv7bui*ufszt*/t(v 2pl 3vj w 2qpb 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 ox4lua.b.45.hh zc u h7foxkf+utput of 120 hp. How steep a hill can it climb at a constant spk fl.h u.f 7czhhx4bo.+x4u5aeed 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 32;pbx voc0iw,y6o d7s 10-kg box along a level f2vxoo iwb6d s yp0;7c,loor at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a5j0lg2 o.xeobus3 sy )w7fkp: 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/h) bumpers” that are de:nu8 cz5g g ,lz9ps s,2it;zunsigned to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested byn z 9:ztnpgz 2,ssl, cgiu5;u8 ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the fuir/1qqiut* ri *)+yx irst shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30. iqr+)*uqu*/1tyr i ix0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s fa.e1xb uu 5zao1mous long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he nob au eux5z1.1eed at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped g77f)hfo jlifw q465 mtrack shown in Fig. 6–39 is to remain on the track at all times, even at the very top of the loog jhf7mfwol 7)56q4 fip 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 jump tv)bsgb ,.5vzing from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his tervs z.)bg5,btvminal 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 6q: q:naccupciz+ ne7 3:vp q7L whose other end is fixed (Fig. 6–7 c+:n uaizvq3pcpeq7q c6::n43).
(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 2)bea)+ft ja.y- ys kwohl;k*to the top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 l;tjok*fey2.+)waks)-b h a y 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 : sffpdv+,hyn,) 4cv,c9 q1co v/rk-jt.xjrs 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 can move 47,0y88xox eebp+l w4o76f 00 people per hour. If the average lift carries people about 20oyfp xl48 8+we67oxb e0 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at t/b v +(gu6 ,o(.idy9 xkrzcfqxhe rate of 650kg/s and falls vertically 81 m before striking the turbine blades. Cdic/.9(ru+yv q(o 6xzgbkx,f alculate
(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 vertical loop (Fig. 6–4su/ szbh*67 fm4), 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, t h*mbz7s/u f6shis 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 directly into ka1re 4lc rf(u*72mczwork, how high could an 82-kg man climb a llk4ae 2m7cr1*uf zcr(adder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upwa9fcpzeaj1 i* ,rd 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 compresses--i+ rz+hpo7peql0 qz 0.60 mm, and it tells you your weight is 710 N.hprl qzz- q +0i+p-7oe 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 swings out overq9:p.j.x f b5 gksydb- a lake (Fig. 6–45). He releases the bb .s kfd9q:j.-5gx pyrope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a verticalk* g1ynj rk 8-brq-*nl distance of 5.0 m in 9.0 s. What minimum power output was used to accomplish this feat? * gy*qlr-8n-kjr1bkn   W

  Some electric-power companies fag 2dsx. x)h)use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store the eneas g ).x2)xhfdrgy 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. Whaxf 4k i+jr4,ddt is the spring stiffness constant for each of the two resulting springjdfd,4+4ix k rs?   k

  A 6.0-kg block is pushed 8.0 m up a rough 37l1px1z ;k6mw*uahpog .l ;xpm hd:: g3 $^{\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 iz9 1u ur:ho.pvqb38 jhuga,l +t take to accelerate fru+b:z9 qog h8vpujr13l,a.h uom 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 patient walks4eyhl: (nzf gw*b(,6ty ky/f q on an inclined treadmill (Fig. 6–46). Estimate the (wkq/4ze: (l, f bthfy*ygy6n power required from a 75-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 vertically upward a distance of 500 :fzkhr5.j 5fj m, what was its velocity when it left t:rjzjf 5kfh 5.he 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 on h2h*)c/h e na8e+mssf 95kg/s (a) If this water wheel is set up to provide electricity output, what is its maximum power o e +)82hs*hse ancnh/mutput?    W
(b) What is the speed of the water as it hits the wheel?    m/s