In what ways is the word “work” as used ine .+ruveihv+tjgle (t;b/3re5pze :s qp 3 1z: everyday language the same as that defined in physics? In wha;jpv5lvegbu1 :(thers+ z.zt:/+ e3 eerpi q3t ways is it different? Give examples of both.

Can a centripetal force ever d gf s.1g.1pghpo work on an object? Explain.

Can the normal force on an objectboul 1pr it9b2k6( 5hn ever do work? Explain.

A woman swimming upstream is not moving with respect to the eftj5v,tqc9/ shore. Is she doing any wot,/ c f5qvtej9rk? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? [Hin(*g11j7yagxf d aelxdza/ , 9zt: Consider what happens to the dishes when you pull a tablecloth out from ,a a/x* xaz(9 11gdlzy 7fdgejunder them.]

Why is it tiring to push hard against a sol,-2;k wc( :7wm y3c , imfkezbsi0nunlid wall even though you are doing no wor,ic03il ;m-mw keknc: n,z2sf yb (u7wk?

You have two springs that are identical except that 5oxdpkf-j2 rcn:p*5 espring l is stiffer than spring 2 p5: ex jfno*krcpd2-5 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on a block that is free to slide otez kt x7ky805n a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time iyk5xket78z 0tt has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational yx,x9 ej)7 ylos)y.cd potential energy change when you j syxc, .9xydejy7)o l)ump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all with th7+ /lo v thfc8:pfaae(b) bu;he same speed but() p a:fo ul;+ba chtbfe7/8vh with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h abovex /iik7pz0j8)gk -rsm its lowest point in two differenki k78x)-rzjgim sp0/ t 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 equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you comp.ip,en q5;o du 31 (k,zrxucilress the spring by pressing down with your ou3 q plieuz,( ;,1kd.x5n richand 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 steel hh: m0 i-po(m0j* rcx oej,.geal63jq wire (Fig. 6–33). 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 pu(eqgrlpx c-om,jj30 oh:.6aie j*mh0shing it. Why?

What happens to the gravitational potentia6xp5 r: 3+ pdgpc8ykscl energy when water at the top of a waterfall falls to the pool b g85py:rk+6 x d3ppccselow?

Describe the energy transformations when a child hops around on a pogo zptf,; bg2ve 4stick.

Describe the energy transfo4 2b0 rcikgvp1;azde4 rmations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a 02 i41p4r;k ezgvbcda snowdrift.

A child on a sled (total mass m) starts from repenqm7cz7,od 5)ymu4(m eb 9r st at the top of a hill of height h and slides down. Does the velocity at the botb)u9necmpm y5,4eq(rm7o z7d tom 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 (.+w b5bvbopcl pq:o:z+ar8 ghv,: nwx 9ao +grather than stepping on top and jumping b :hqavb(9pnv:+ gco+rwzlgb oo a+,:5x8 .pwdown on the other side. Explain.

Two identical arrows, one with twice the speed of the other, arevmsuju 9 os:z7 s4v+g; fired into a bale of hay. Assuming thz9+4svj v: gum 7o;ssue 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 ,l1;h flhcvnpo765.: bz:zb ikzf cb8terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why 5lfpzo ,:bc nbc1 .fz: blh;zih786vka grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its o-vxr 04/6 ikh9e:ltve au)mspriginal height? Explain.ilt69 p h e-x)ve4mrv/as :0uk

Suppose you lift a suitcase from the flojx*f-ri9yju r njs 0+2or to a table. The work you do on the suitcase depends on which of the followingnjj*- 9+ i xsyruj0rf2: (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 the power needed rather than twir b99 o 5dpl4ud2v)qhe work.

Why is it easier to climb a mountain via a zigzag trail than to j21hn vmb3)unclimb straight u2n mv1n bu)3hjp?

Recall from Chapter 4, Example 4–14, that you cano7 wfj0mb h:,f use a pulley and ropes to decrease the force needed to raise a heavy l7 :jf0hf mo,bwoad (see Fig. 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 2a/8mjsr r9/aj65-kg pile driver falls 2.80 m?j/98m r/a rajs    J

  A 65.0-kg firefighter climbs a flight of stairs o53tcew hco 6/u5u(ix 20.0 m high. How much work is requii (toue5hw u3 56coxc/red?    J

  A 1300-N crate rests on the floor. How much work is required**3c9p 15 diawwp ugyd to move it at constant speed (a) *ppa3 d9yci5udg*w w14.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the gdiz92h 69ut)lst* )ix7llb)ch( eeagz +xh,movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effectil9sze ,6hbed) cxz uah*)lh 9i ( g2xtlig+t7)ve coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a f*opfih (r9z+/9ac ikborce across a floor at a rate of for 7.0 s. Find the net work don(9zf*ki+oc9b/hip ar e on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table.iy c.i8eut33 a fgo/q3n tk3*c How much work is required to stack them one on top k/tu c en33tya.o8 3iqigfc3*of another?    J

A lever such as that shot- 1y pciy94riwn in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of 1ii-ptc4 9yryoutput force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° incline and is kept from accel fnk:)2ia*+ z/ rcnpzlerating by a man who is pushing back on it park+ z nnil)rzaf* 2/cp:allel 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 g/ ;+:bdxe)kj-n; zm+h cbps ;yim *vnqive a helicopter of mass M an acceleration of 0.10snz*k +x-;c:be);qmj/m i nv;d h+bpy 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 the distance ahacrzdp1u* rt(.x/f uekxad 35*df00xis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as sh- kiy8f-r0cdrow f0(p own in Fig. 6–37. Det -y8w-kfirpord(0 f c0ermine 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 on a particle lkv+ lt(vuq9w53b m-l 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 masl* z3cn90d 4mwdh/ mqk8sotb2s 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, (*arvh9z kyk5by 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 electron yj vr1o2,qp7/ 0f:yftmxo8pa5 ek*r f$\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 to7kk b6 ckc;kv. stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bjxc rt1n/ x37xt 37xd9wtzjp2 ow whose string exerts an average force of 110 N on the arrow2tp3x t t xjx377d1w9/cjx nrz 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 mov-socz.9n5 b1zsum mz: es a fielder’s glove backward 25 cm when the ball is caught. What was the am nbsc1m95 - zu.soz:zverage force exerted by the ball on the glove?    N

If the speed of a car ibr fk5lzr( ;4a-biw4t s increased by 50%, by what factor will its minimum braking distance be increased, assuming all else is the same? Ignlzafr4(r ;kb-4t biw 5ore the driver’s reaction time.

  At an accident scene on a lj uji( l7zjp:7evel road, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car(77ijulp j :zj 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 kg is+ -all/)ipj v, g;0dnobvcg u5 pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the averagaj-u0 vvic ; n bp),/5+lodlgge 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 straight86il2rbebb + h up by someone who does 80.0 J of work on it? Neglect air resi2ebb8h i lb6+rstance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration haw2w1 -sf7 oy by a single cable. Dete7yw2woh1 as-f rmine
(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 stiffnessvsc 8+q uu+w,x constant, k, of 440N/m How much must this spring be stretched uv+,uwq+c xs8to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2jijgab7; z yk6pl +3m, m higher. What is the change in potential energy?g,6az;kp jm3 7y+lbij    J

  By how much does the gravitational potential energy of a 64-kg pole vaulter chanuevdt 6+tr/cy(n3t4pywy*;j ge if his center of mass risesy3yvt tj e+/;yw up4 dn6ct*r( about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it slfr ) dic89(do tcp5:mtrikes a horizontal coiled sprin rfpodclt 8cd5 )im(:9g 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 grounf4abyx:z 1ids64r )s kd so it is 2.20 m above the grsif)szy146:r bd 4 kxaound. What is the potential energy 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 climbs to the top of x :48 dvvqdug.a 3300-mgv4: du v.8qdx peak.
(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 lrn(0*mdgg1fb)r i3c i /li9u ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg mass is now attached to the enguild 9 b*i(/1ic)mflr r gn30d of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vo5dz f0 kc;ft(ine hanging vertically from a tall tree in the jungle. How higd k(ofz;5fct 0h can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slidihk8egtk3o h cm+r .)+x(h)1prztyln 6rx;+ges 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 acx -pnzm9 x)i3 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 enr-j u*)ygc9j 3-whwc gergy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and cro cc*y9)3 wwjg hr-jug-ss the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platfor 3lx0jobbfu9:m with a speed of:b3bx9lfo j0 u 5.0 m/s. ($\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

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

  A vertical spring (ignore its mass), whose spring stiffness constat gw(h 9sh(gg8nt is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward 8ths( 9gg(ghw 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 aloiey0 hh8+fsd -ng the looped 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 mushyfs08 +dhi -et it be released?    r

A block of mass m is attacwm)0*b (-x lqyj+va ushed to the end of a spring (spring stiffness constant k), u-s+l *0 mwy)bxv a(qjFig. 6–40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied tq6 6/f 5(xmx3jfxq aago a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assqfq(6 3xxg 6fa a5jm/xuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster cauznc- a( ::ryir shown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calcuya izuc:r-(: nlate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown()ig3v *k asy 3lf-f7hr8o-c av* rjxs with a speed 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 h+e 6k3wud;*tr sjr* velevator 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 passengers undergo an acceleration of no more than 5.0 g when brought tr**hvdj s;w r +ue6kt3o rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.8 qck0 9os5)frv $^{\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/ehkbv2 :cz0n6 h in opposite directions, collide head-on and come to rest. How much thermal enerb2vhn ze:k6 0cgy 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 z per8s0 )b;rm: n:skjt)lie 1with a speed of 2.2m/s How much ther)spkmnrl: s : ei0;)1jr ebz8tmal energy due to friction was generated in this process?    J

  A ski starts from rest and slides dowi gy,8 h*vtaoruig,uw9kd;:b3 ql 1 8dn 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 tj4 ;chz2.o ef3 e.5s(xl dkjkmhe 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 bveq:zy9 46i hyq0/ clnack to a height of 1.5 m. hz:9nl/6qcey4 qy0vi
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a co 1wvzj-r94has xkb85 5s j4rrnnstant horizontal force of 350j44 8jrzkv-as 5rs51n9hrx wb N. For the first 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 point 1 with a speed of If0cfzv1 gu*ws *- 6hshk the average force of frictionu*z wh0g6 1 csfk*-shv is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot ofph;spr 74bjs+ 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 spring (k:/w 4r0nk kel i3gha9.vz:lmb=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 p3n a: e.r/940 mbkw h:lkgzlivosition before stopping and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is fi n)sq3ibg:m0drmly 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 position will it stretch on its first swin3dn )si0 g:bqmg?    m

  Early test flights for the space shuttle ( s38z(lelfwzy-mq-mvp 8 5onused a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing swmp3vzzsle5-qol(ny - f88 (m peed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-knvtg3/rbjel:dikrn5 ;l+o 8 /g piano to a sixth-story window/;jr3e:l t ion+gn d/kl5 br8v 16.0 m above?    s

  If a car generates 18 hp when traveling at ah(1mv; z1vh+:jt u*sr n+b evn steady 88km/h what must be the averat j r1*b(; zhn+hv ue1nvv:ms+ge force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car atlge*1n13g zcna e :*gccelerates from rest to 95km/h in 7.4 s. What is the average power delivered ggg:1 eel1n3z*tn*a cby the engine?$\approx$    hp

  (a) Show that one Brit(6*hu tyl54, 2qc smw d+eivqj1xji1tish 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 “kilo 712z p6 bckjjukqp k280zx+yrwatt-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 65km/h in a8fzw9uf -iq e0bout 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75kiw f-fuz9q e08m/h.    hp

  How much work can a 3.dtmp *r+fke5hj m c,400-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 thisxd)onb,s b 434i3myp9 :kjkuhk.r5k c motion takes 1.5 ryks5chm bkpk)j,4.i4b:uno3xd 3 k9 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg o8iwbobmj +(w nb/r-m+a8 -hgnf water per minute through a height of 3.60 m. What outputhbimobrnm -8 w/++(a -n8wgbj rating (watts) should the pump motor have?    W

  During a workout, the football players at State U. ra071 u( ax7q9hkjt:y exat9 pl+hem -fsn up the stadium stairs in 66 s. The stairs are 140 m long an(1 ektjuyh:9qmtx xa7s79p f eah+l0- d inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6oe9qc3ruhg6 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 tj)+ nv wof-qq3uhzm .ry d/(.maximum power output of 120 hp. How steep a hill can it climb at(ntjo dv+f.) 3 yq/hz.ru-mqw 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 drajtvmj- j)4/iujj;wzd 59 gz aud;yo*: g a 310-kg box along a level floor at a speed of 1.2m/s -;zv*)d /utijzj45 jgj9 u d m:yowaj;if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.0mj phnmyx9s13 i0 6c8nhpxg67 $^{\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 desig9zmnd.xh .r 6oq ,ak2 5uj+y)qalt rj7ned to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently ulx r.9t).nro aqj, j2z5+ 6 dk7qamyhdeforms 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 by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the firsedt x ij373,q9kqt8;cobk ee* t shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shel383ic;7 t jd,q qoxkkeete*9bf 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 Owenss: nwq9.znki5jrdsc,bq w(jbzh9 ; (; ’s famous 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 j,;r;cwqj9wnz ((hiq n5 b. :sz9ksbd 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 slidzxu b . z6j6u;1i5mbqbing without friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top 1bbuu6mj qxz.zb5 ;i6of 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 j.diwo9yef 62+4xa iiv;cxs0 kumping from an aircraft without his parachute opening. He landed in a snowbfsxc4a ;2vx +wy 09k .idi6oieank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s 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 end is ftc jb(( xunb.2ixed (Fig. 6–43(.j2cb x(ntbu).
(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 ,3l wg,,ublr8 +t vxh8ldrt)fe b*lt5a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 23 lwt,l8brvxf + tu)gl3d te,r*h5b 8l,00 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 huge spra 0lkq-giv:. oing ($k=2.2\times10^{5} \mathrm{N/m}$) 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 lift,e8xwmp1x)uc qd ukv: hk-(x:mm55lv s can move 47,000 people per hour. Ixdchu)m-qm55(:x v wxk pl81e,umvk: f the average lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kges f7 *vk(ypux8.khq, /s and falls vertically 81 m before striking the turbine bladesv*y,hk7 ek( 8puf.s qx. 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 circul)623i: npax p(cxqyx9 c)6mr(* nlelxpd*jvb ar vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your wep3n)6xcdrm )9iy2lq x :*a(*jpe xx(n c6lvpbight. 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 directlp +4ujb:g+hmchkz9 (fy into work, how high could an 82-kg man climb a ladder if he+j pz:gu 4cfhk+mb9(h 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 atvl-s: s: 3t946e nvh udz7 xcloyo8/xsd2 (ckq an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside tca +5iv9p grzr9sotlrd p3ia 9(3r5*w he scale compresses 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, what does the scale read a93 93(gzdp wsa rii*v5r +croltr59 apt its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and s+yam f yhkaf+.v3n1o7p1 7obtwings out over a lake (Fig. 6–45). He releases the ro+onvaaof.bkf +17m 7h ytpy31pe 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 rthj8e /uy-sz1o/ 6z, 5ujkxmclimbs a vertical distance of 5.0 m in 9.0 s. What minik8j-orh /yx5z6,/m t1s ujeu zmum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. ((;t0xtse4e6maj g- ykm cuo0Water is pumped by reversible turbine pumps from a low to a high reservoir. T( mtmug-0;t ek(4x aecjyo6s 0o 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 c+5, +w ofml30 d xkd9ad6w3gd w7itk-9d bsvuk is cut in half. What is the spring stiffness constant for each of the two resultdwmf b-+w3ls 0 tdcud79a 6i3vo9g+5,dkk wx ding springs?   k

  A 6.0-kg block is push;3rpek uoqno.fom 7z,32kv t*ed 8.0 m up a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 cqe*ani /*6xs svw/t6s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, 6tsxv* s*an/ wic /6eqand neglect frictional losses.    s

  In a common test for cardiac function (the “stress test”), the patientwobq5i4j mxd k fie)f 5rl6(5, walks on an inclined treadmill (Fig. 6–46). Estimate the powe)e54ikqd5i 56wfr mofx( b,ljr 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 5pd87gj) +qi hfi dgk9900-kg rock vertically upward a distance of 500 m, what was its velocity when it left the volcano? f9p+8h id)7gd giqk9j $\approx$    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 95lr7ws aunt(w-n1b ah:.a* uy)kg/s (a) If this water wheel is set up to provide electricity output, what is bw* lyau ua:1)(rnh.7 ntws -aits maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s