In what ways is the wortu.lycsra0 fs mf9b;*7 2dh74ecdu)td “work” as used in everyday language the same as that defined in physics? In what ways is it different? Give examples of both.tb c0ueftr*sf9u;d4 7clm)a.h ds7y2

Can a centripetal force ever do work on an(72c dz*xte .)g hspyh object? Explain.

Can the normal force on an object ever doifp(4bko (/p j work? Explain.

A woman swimming upstream is ctjl4f62km w 0br0xltz4 80uanot moving with respect to the shore. Is she doing any work? If she stops swimmin4 mcfar8400jlkt x wzul 6t0b2g and merely floats, is work done on her?

Is the work done by kinetic friction forces always negative? fxh(b 5kog23t [Hint: Consider what happens to the dishes when you pull a table2xkhob 3t5 gf(cloth out from under them.]

Why is it tiring to push hardsu+4pf fqb(4a against a solid wall even though you are doing no work?q a s(fp4f4+bu

You have two springs that are identical exzn;sq/ot6 t1 br+gz o2cept that spring l is stiffer than sprrbt;+go1 q6 oszz/2 nting 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 horizontal force o 6vuz v+n*6 g/u: kfmcbmf1yw6n a block that is free to slide on a frictionless surface (Fig.6-30). The wc* 6u v+66b:ymuzkffg/ vmn1 block starts from 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 your gravitationaloq;/uahi0r*pn 2lr2 i.dez)j potential energy change when y2n)0 dupar.z/i2* i;jeqohlr ou jump as high as you can?

In Fig. 6–31, water balloons are tohhqe: tx4s/i3ssed from the roof of a building, all with the same speed but :xshi4 tq3eh/ 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 heightn)/pqfb x3qx3dmo fp)g 8h10m 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 directed downward along the trajectory. Which launch will dmx13xmh 3qfp )n0 fo/pqg)8bcause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress tviqcx:yek k3*z j+j55he spring by pressing down with your hand and thexjk q*+ e :yizj3k5vc5n 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 z n/q t/odt f/;bl 3o/rede3h+wire (Fig. 6–33). The instructor pulls the balltrdle e h3ofzb+/n;/tq 3do// back and stands against the wall with 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 potentils b( 2vyruxh+1,cl/ral energy when water at the top of a waterfall f1rr,xuhl2 /(bysv l+calls to the pool below?

Describe the energy transformation,o*o;na: u vnos when a child hops around on a pogo stick.

Describe the energy transformations that takonthqm1,/ 16 ejx-xpve place when a skier starts skiing down a1jp q6,ex t mohn-v1x/ hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) startbg0ri/yi q)j (s from rest at the top of a hill of height 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, ang)yii /0qb( rjd (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather t46g*xbeic5ry) c0t dz han stepping on top and jumping dote0grc)dc 6ziy45 b *xwn on the other side. Explain.

Two identical arrows, one with 25xa99/ mbbqjg -rmm5qkjx:stwice the speed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrowsj5r9 b qg:s x bja/mmqk9m5x2-, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in termyu bk(vg,z* 7vmo i8y4s of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be wound u8g 4u*b7ioyz (kvvym, p.

When a “superball” is dropped, can it rebound to a height greater tot fl0x4u6o 0iiekolx y o16:9han its original heighou 6i0f1l46e 9xxokt y0o l:oit? Explain.

Suppose you lift a suitcase from the floor to a table. The work you do on thelz)zkud:j.o g8 s( u5ya4 5yjl suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (bo8 z ()ljyaukdlyguzj5s4 5.:) 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 thap*+j.ibeixmmsog/e ,kqo4v:87 /s l bn the work.

Why is it easier to climb a2 hwka(+ g8xkqe -o4ga xs0mk1 mountain via a zigzag trail than to climb straight up? x4 8wkh o2gqk1-maxka0sg+e(

Recall from Chapter 4, Example 4–14, that you can use a pulley and ropes to,m x4-9 wfsin vj;7yrz decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account -y;jmw ,is7n 4rz xv9ffor this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile dr*2myx7cn9 erwiver falls 2.80 *cwyr27n exm 9m?    J

  A 65.0-kg firefighter climbs a flighto) go +hvgyq27 of stairs 20.0 m high. How much work is requgq+y2vho)g o7ired?    J

  A 1300-N crate rests on the floor. How much work is requ-qxg ijqs ;u s5kk+,/hz4q3q5gnea7bired to move it at constant 4 uek 5+q g3sb5qkqg7-,i;/ anh jqszxspeed (a) 4.0 m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kg crh ggg-,yn 8xb(ate 10.3 m across a rough floor without acceleratin8g,( ggxy h-bon, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is acsjbu8ccn8 (f 2g.pz,lcelerated by a force across a floor at a rate of for 7.08bp c. 8j,c2f(sulgzn s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with5e hn)9aap m1r mass 1.7 kg, lie flat on a table. How much work is required to stack the9 pha)nare 5m1m one on top of another?    J

A lever such as that shown in Fig. 6-35 cang*g1n3 cp0h lt be used to liff objects we might not otherwise betcgl01g 3p*nh able 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 3.6 m down a 28° inntv12)zhqea.i,6nz*r u f 1ugcline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36*in ughzf,ueq) .rv2 1zat1 n6). 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 req-4ao a(n ug9lquired to give a helicopter of mass M an acceleration of 0.10 g ul-9an( oga4q 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 distanvo)h 9 k xyrf3s1qm+j4ce 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 atx w6/fj.f/mc -ok56qt3l xpsxis, varies as shown in Fig. 6–37. Determintj .pc/xkf ml-fo 56qxst63/ we 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 partichv5y+ r5eq efgnb045o le 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 mo8syw;o/ rhtf3b r1gmg) -6qpg lecule, 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 ar/ z7 .k3*lv*is(cg9jlfgi3ru p sryj8row is doubled, 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 required8pa/h0ju vxuy*d. 3fbrq d: s1 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 h ov 8zd-9z ; jl2bv8gpfalg-; v9fa6pstop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired tl) zz;k/2+rrpjyf 8aadu0 x1from a bow whose string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow a;fj) 2z uatazd+r /l1ky0xrp 8s it leaves the bow?    m/s

  A baseball (m=140kg) tri *rjqmcnje9 ;/j/:te:9sqe aaveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the aveqejj /ic;:/9rs en tqe9 *ma:jrage force exerted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor will its minimum brvqv2 5c-k y*cn vd/i*qaking distance be increased, assuming all else is the same? Ignore thecvy-d5q i*v n2v kc*q/ driver’s reaction time.

  At an accident scene on a level road, investigators measure a ca9-8njrq5y 4j+. gtpm-v 2 ubvhcr ihc*r’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 dete5r84hp-mtq i c-r*v hvyb2cu+n. 9jg jrmine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg iz92 xn- y1 fpauw)ve9os pitched at 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 the distance between the plate and the pitcher ix )9o w2pa9zy1nfv-e us about 15 m.    N

  How high will a 1.85t / :aybtxmubb ;*2br:-kg rock go if thrown straight up by someone who does 80.0 J of work on by: / a:xb2b t;btmru*it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m verticallyu/h, h/z we/jv with an acceleration by a single cable. /vh whe/,u /jzDetermine
(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 stiffnes qohmo(;9wc*+umj+ c*nhw b t+s constant, k, of 440N/m How much must this spring be stretched to store 25 J of potentiauc h (jwm* h;+tbq*++cnow9 mol energy?    m

  A 7.0-kg monkey swings from one branch to enr.abtg /x+/ another 1.2 m higher. What is the change in pot/xe /t.ba n+grential energy?    J

  By how much does the gravitational potential energy o v(dmc8k2 +pdk:w9.d4koofz p f a 64-kg pole vaulter change if 9kvdpwd ko+cfkmd 28.4o(z : phis center of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 kml1yo2ahd3;e eajc4 3 u/h when it strikes a horizontalco43j 3e ea1 2uhylad; coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground so it is uhigm0 r :z0u22.20 m above the ground. What is the potential energy of the book relative to u hgiz0m02u: r
(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 au+s s5n7hbb7x7p xum4/ k+qiqn elevation of 1600 m and climbs to the top of a 3300-m u/7x7bx7 4++ ski5msquqbhpn 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/s9i3aa6qdnx-b ,c bn/m hangs vertically next to a ruler. The end of the spring is next to the 15-cm mark on the ruler. Iin/a3 nc ,6s9d-bbaxq f a 2.5-kg mass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/sug,n t (eyunn1a0d+y;) and grabs a vine hanging vertically from a tall tree in the jungle. How high cd;(y ,10yae+n nguun tan 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 friction a u2ul/us :/ wt-i+ pjvtuj mm:0qd8b-h,aac)less 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 frict/gl5s3q j5z w4ed8qri+ vep0 uhdv +gfmc4,+kionless 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’sz/ic );q:fh :*y uveanra8fs9 kinetic energy 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 aua*qrh)c9sfeain :v ; /fz8y:nd cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps v ftcv1j,/; hnkertically upward from the top of a platform with a speed o/vchn,jk 1t f;f 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 sr86q esu qpl:9pring 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 a 0.30-kg ball when releaseduqers9 q6 l:8p?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction a sr n+.5uh:doolong 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 must it be relea5rn.:ou+s oh dsed?    r

A block of mass m is attachefeejn-::kxj+ t ,qvz5d to the end of a spring (spring stiffness constant k), Fieq +-t ,x5 :ejvfzknj:g. 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 ti8q uqmas/f x(a4/-dge*o1p j(rxh ;kjed to 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, assuming Hooaju- q8/mrh;jx /(pof kd(eaq x1*s4gke’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 dragga di5o/pvz 6,red up to point 1 where it is released from rest. Asrv6o5d piz/,a suming no friction, calculate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed obvfr* le.h-h ;f 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 bo)9nac) : ezycy-)osnox*7ps i 9 4kavbttom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calcul:yzson4b ip c 9)os)ky9avnxe*7-)c aate 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 to ovt .yr+ib 1 na0w4,j7lcq:;fnvig /zcycle 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/h0 *.yyg:rua c koex)pc2pua2- in opposite directions, collide head-on and come to rest. How much thermal epo2-0caay. rpx) *uykueg2c:nergy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high ah 5i.y96aleennd reaches the bottom with a speed of 2.2m/s How much thermal ene he l5a6.9yinergy due to friction was generated in this process?    J

  A ski starts from rest and slides down kiz9br zc //3oa 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 tha7 rgcu.-u zdotcu5 y:z )y-0sbn:n/ue 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 ,wthq ( vvs:h0,wbgc 6height of 2.0 m, and it bounces back to a height of 1.5 m. q bhvv 0gcs,, t(w6:wh
(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, start ;i1bmtsb c(xl3(tl 2iing from rest, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionle;3 xlc(mibl 1i(bt2st ss, 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 wnf,avz 1g,n,.hs-unc ith a speed of If the average force of friction is equal to one-fifth of its weight, u,h-sc1v ga.n, nz,nf 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 steady + ;hzwta /kmy1upward 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 horizont- q j6/ye7w+fhl(hq2ibp v*bcal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between the block and thfwqv76-ib lyp*b h+e /h(qc2j e table?   

  A 280-g wood block is firmly attached to a very light horizontal sp58gt(e1lxl: ( uxy zuzjwx*9uring, Fig. 6–40. The block can slide along a table where the coex:u w(8(z1lgyj* et9l5uxz uxfficient 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 space shuttle used a “glider” (mass of 980 kg in pysz7l(:,ysg2pf8 swcluding pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a s8gs wypsz:p,l(2fy7 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 315-kg piano to )jx*7at/ipus f o8pn0t ,wy,ya sixth-story window 16.p/t y s y,of8,w0ip*ua xnj)t70 m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h wd u4s 99exrgw b//,rmwx:) jachat must be the average force exerted on the car due to friction and ai/,rbex:w ujw/gmdsr99 4a )cxr resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What isd/ tdu6 f ixd,0/mjm,d the average power delivered by d0 /mti xdfu/m,6d, jdthe engine?$\approx$    hp

  (a) Show that one Briu )u dd:6;pxxftish 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 expresse2:c gvfc0i ;uvd in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices tha:ug*h:7 7b/uqlxq j xtiwm21 wt her 1150-kg car slows down from to 65km/h in about 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 c qht:xl bjx7w u2m7wg/:1qu*ionstant 75km/h.    hp

  How much work can a 3.0-he ldczt;pt+;m d 9 tyyx62g*i+p motor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this mol2n1 ;b8st2bz. ib b/que:bxb tion takes 1.5 s, what average power was developedu2 be nbsbb2l q18tb;i/.bx z:?$\approx$    W

  A pump is to lift 18.0 kg of wf ,/rzp7kg3vbw/ld)b )dzeq; bn ow+0ater per minute through a height of 3.60 m. What output rating (3/7,orfq+k) wnp vbg;/zbwe0b )lzd dwatts) should the pump motor have?    W

  During a workout, the football players at State U. ran up the stadium 9 cmildh x73y8stairs in 66 s. The stairs ar8c3dl9h i7mxye 140 m 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 climb a 1aw3shpc* ib e2* u+*2lzp. -zvxuiuc 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 steep a hill can it qfh)nl i h*j61y5u7fjclimb at a constant speed of 75km/h if th*yf61i jhfnjl5uq)7 he frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to br (jycm 7xzh3m9 s;6jle able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of frictijrzy7 jl 36(mmx; chs9on is 0.45?    hp

  A bicyclist coasts d 8tz(gowt,y9p3h rp,f4faq i4own 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/0ijn:z +prl l1av.8 yoh(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 bumv.:+nply al i08ojz1rper 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 tvwy-6v:7m,m 1f pjkgfhe first 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, and6wv -yfg j,pv7 :f1mkm 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. 6–42) in the 1936 Olympics 1kteydi- z9n;shows that his center of mass rose 1.1 m from launch point to the top of the ar1zyi;nd9-t ekc. 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 without frictioa)6y2 d9pzmve n along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very top ofe6)mvda2p 9zy 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 his parachut: -sc wyd.n9lme opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s9ns cmw-:dyl. 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 f 9f-mee8vg g 6t8e2+ vmgt(qatixed (Fig. 6–43)ggv+ -efqemm6etg9t (28t v 8a.
(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. Thexe 5 8kvlwl2yx-l)(fa climb is made in 5.0 h starting at an elevation of 2300 y xlv fla8x5k 2-we)(lm. 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-3bw u,h.t9l+stvk xf)3 rczd a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 4,k;m.qfav ixk)u a. 1b7,000 people per hof am;i1vx,b)kk..qa uur. If 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 650kg/s and falls ver plpqh321 d;jhtically 81 m before striking the turbine ppd2ljq; h h13blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertrxiaxukcwfj6b,4 hl z )9euf4;(i1 hn1g2m /qical loop (Fig. 6–44), the difference in your apparent weight at the top of the circulazh n xu bw4/2g( ;m)kf1ux1q96l rjf,ie4a hcir loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert a candyy,xj e8-b sy 77pg 3via;+jptf bar directly into work, how high couy;y3sx 7f-pagpv,8jejit 7b+ ld an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward b.qwrp b 37g+bangle 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 scaleul2 he(rmfo1m74,gw6 vh n 2:gmh b3wn(g t-bi compresses 0.60 mm, and it tells you your weight is 710 7nf -,hwigt(ue1gn2bl mvr6 bm:gom hh 2( 4w3N. 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 5maoekh l2b257l3 w7e/ zit y5bm/s grabs a rope, and swings out over a lake (Fig. 6–45). He releas7273o m5b/wliyeate h k2b5lzes the rope 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 vertical distancekj a7d7uhg4w, of 5.0 m in 9.0 s. What minimum power output was used to accomplish thisujh,ag kw7d 47 feat?    W

  Some electric-power companies use water to store energy. Water is p.7 bjfi:hci p 3tk9 u4df)w(cfumped by reversible turbine pumps from a low to a high reservoir. To store the energy produced in j: p94fdf3.7c itckf)h(b w ui1.0 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. What qw o .+3aqcewe)bid8ofl ,45q is the spring stiffness f,.db8wq4)+eoqo 3lq5c ei awconstant for each of the two resulting springs?   k

  A 6.0-kg block is pushe u-y+ /y1nn/bdkbiop( d2 nzvmu/s5j/d 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 s, how longb7fm8 8yo:f2 yh6r em3nh )jyc will it takem)f :o fy6y hnyhr8c3be7j m28 to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac function a( u6xjzo(1xlih 5,s agy(lc 4(the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-x(h a,(i u 6xjl1y(clg 4zs5oakg 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 04eggvnt :lm5sh ,( uvp:g;fja 500-kg rock vertically upward a distance of 500 m, what was its velocity when it :vgg5 l(p:nuft0; g4sj,meh vleft 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;ov5yu2q rir0lo / /- o5g(rngn) wbnq m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity oun0/2b- qu 5;g5qwvlnnoyorr giro(/ )tput, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s