In what ways is the word “work” as used in everydaylgeaxr7mx2 : mcz30* r language the same as that defined 2zc0xmrx 7eg3a: l*rmin physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do wor j ;teu3 8bv;ka7llnn.k on an object? Explain.

Can the normal force on an object ever do work? Exp2ke 1zh 6)ksxkt3+5jb tpr*yilain.

A woman swimming upstream is not moving with respect to the 2o 4fc5 ejt(koshore. Is she doing any work? If she j t2 4c(eoofk5stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction6duep0qevyh6/ 72vvh)c 3lko2/yvv d forces always negative? [Hint: Consider wha7v)/ev6c6 v lov2qy dk3dh/y20eph uvt happens to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even t3 d3npzhpcz8n 3; teiwn; og0(hough you are doing no wor;n 0i(ppn33; 8o thweg3dcznz k?

You have two springs that are identical except that sm7t /t y5tkczpd4,f) apring l is stiffer than spr 5kt 4zpmd/ctf,)ay 7ting 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 on a block that is free 2pakkg a 8top9m/ z l4c-kk54o(qm.tlto slide on a frictionless surface (Fig.6-(okpac 9mka.q5 l-/4zk2kotm8 plg 4t30). The 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 gravitat*ly -o mvhj(vd9m a60dional potential energy change when yhvvj0(d 9do*ma-y6 l mou jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roof of a building, all widm4(y2to3/y ylvcq6 k th the same speed but with different launch angles. Whiv3y4ydk6/toyq(c2 ml ch one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point9s*l) fkn5cq2m 0,j6j ehn chi that is a height 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 m0,)65jkqc2n*f9cej hsi lhn 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 compress t9cycv7wp+ j+kgk3 +h3 4tu- ixu emm4ohe spring by pressing down with your hand a3yhm+4u wk+ct+3 mogi xk7v94pjc-e und 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 wire (Fig. 6–3onz n7n85mvoyy b63lpzjx2z 9c) ,8 jc3). The instructor pulls the ball back and stands against the wall with the ball ag5l) ,znnzoxc9ncym83ojy pv bz76 2 j8ainst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravita glgzv:4+6+q:opy lmutional potential energy when water at the top of a wate +gzygp+6: oqlm:uvl4rfall falls to the pool below?

Describe the energy transformations when ahtfe*qbh4iw:re 5t 5* child hops around on a pogo stick.

Describe the energy transf u6tyfgas/v* *7lj3.)rgptl z ormations that take place when a skier starts skiing down a hill, but after a time is brought to rest by striking a snowdrirg v/jyz*.pt gut )fsl6la73*ft.

A child on a sled (total mass m) starts from rest ak yl u(ih5hp29 hrkojg z9(a56t 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, and (l96j25rh5 (iyuzhak( g h9 kpob) there is friction (deep snow)?

Seasoned hikers prefer to jh8) jglye ns4 m74j)iya -sk9step over a fallen log in their path rather than stepping on tyk )hnss) jly9gm48 ji4aj7- eop and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are.4 mhq4z41repm tvf1i fired into a bale of hay. Assuming thz114qp 4.mrmtev hf i4e 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 energy, (ad. 7 ejq kdm;42phc7re) ignoring friction, and (b) taking friction into account. Explain why a ged.r724mp ;e dq hkj7crandfather clock has to be wound up.

When a “superball” is dropped, can iz o,4*zd y9mpat rebound to a height greater than its original height? Explaza oy ,z9p4dm*in.

Suppose you lift a suitcase from the floor to a ta1 ip, i/f m;sajbyv4;able. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated path, 4i,f yba;s1 /jmv;p ai(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 rarz(k7c(ajr v* j h td7;v(y)p.xyewx )ther than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb stra igcb,(st +p,iight uit g+ ,ips(c,bp?

Recall from Chapter 4, Example 4–14, ;;hy ra j 5fwt-i8apbe/gp3k8 that you can use a pulley and ropes to decrejr w/8y;k 3 phetga;i5a8f b-pase 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 for this, using energy concepts.

  How much work is done by the gravitational formhgigbt-ac8::+3 ol xce when a 265-kg pile driver falls 2.80 xc8+lahg: gi:3b- mot m?    J

  A 65.0-kg firefighter climbs a flight of stairs *b2a vn xsr5c.uf02c2r tp7ci20.0 m high. How much work is required r*tsnc.2rp7i bfa0 52uxcvc2 ?    J

  A 1300-N crate rests on the floor. How much worv. wg*9 t0gonlk is required to move it at constant speed (a) 4.0 m along the floor against a frvg og09 wln.t*iction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (-tab6re2m:/8 wx vfj 6otb9nhhorizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction was b2:t8x tvf/er a-o6nw6j hmb90.50?    J

  A box of mass 5.0 kg is accelerated by a force across arb0 7kqc5qo 6j floor at a rate of for 7.0 s 6 r5c7jbkqq0o. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat4a,9:sy 7mjzoalf7,zhdj xu2t 9j.q z on a table. How much work is required to stack them oyujdts:9,xaq729m4z j 7 z fzhl,jo .ane on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff obuoh97nyx6k eo -/ky-fjects we might not otherwise be able to liff. Show that the ratio of k hy-n9o/ 76k ofyue-xoutput 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 anmhb10 r.e4e y 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 kinyb1n4me e0hr.etic friction is 0.40. Calculate:
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a he1 im.kl gir*q7lyc1e;cn- cb/ licopter of mass M an acceleration of 0.10 glbe k1;rg-*i7ccn./qi cym1l 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 lq( /fzhtsht/25uvknfgq (5 y3inear 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, vari/q c0 ky9+a,tvpo ifyg+q4l q.es as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10oqv0y+kq+t pa9q.fi y4/,l gc 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 exerteqt( q30sud4*7 +gk psy(jeykyd on a particle acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, withz;v,(166p5 0pgdwco tjir uqr 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, by wha:o rk/j0*oga;y6 yzgct 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 stop321ih; p5abdu c*nsf4 s(e rsf 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 stop a 1250-kgcar traveling at 105k:b d* fyf6:b(jejd ;34any dxlm/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an4jwy.0eg q ir; average force of 110 N on the arrow over a distance of 704;r gyqewj.i 8 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm whn6 q e3el26u+nyv(p9fqbhyb7joh ,4 v en the ball is ca7hoh+,q92(yj6bv4pe n u ebyqnv 6l3fught. What was the average force exerted by the ball on the glove?    N

If the speed of a car is increa fpy iy),+(zsbsed by 50%, by what factor will its minimum braking distance be incryib) pz sf,+y(eased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level roa 3hdtq-u 8tua1d, investigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy da1 htuu3- 8taqdy, 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 (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kgkc ;bc jn7rs0bts+r ,s/ h4l.h is 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 trh.7,bkr; lc 4/cs t+j0snhbs he plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown straight 3bv 9g6 5gt7bmg cf4 0wf7xtgoup by someone who does 80.0 J of work on it?ctgbgm 9 g40ofvg 6bw3t7x5 f7 Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single cabeoz:sqeb* *b *le. Determine*z *oeq*beb: s
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness con72px4h jbnij/n e 2bj742 qpgbbrf*l+stant, k, of 440N/m How much must this spring bjjipjx*gbf 4e2qb7hlpb22 n n/74r+ be stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higherct 5 kh-a3yk6m. What is the change iam3t-y6ch k k5n potential energy?    J

  By how much does the gravitational potential +6j af4zs ,mqqtl3/b9 wskt0 g9z6ikb energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m during the jump? gl6t /zbz934,w6sq 9fks0ki+ t jbmaq   J

  A 1200-kg car rolling on a horizontal surface has speeofg8b m-;kug.gjpj;8 d v = 65 km/h when it strikes a horizontal coiled gbgogk.-pjumj88 ;f; 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 an zepf 2552f0*bbsywj 2.10-kg book from the ground so it is 2.20 m above *pe5f 50 z2nfbswy2 bjthe ground. 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 than*tq b)gp/y+q4f. fhe top of a 3300-m peh*. a 4q+bn q/pgyftf)ak.
(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 al. m1a6 yyv2vdf+-cyl ruler. The end of the spring is next to the 15-cm mark on the ruler. m+df1 6.ayl2-yl cv yvIf 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, i g.h4j0zmxh2ane-o.y s running at top speed (5.3m/s) and grabs a vine hanging vertically fromynj.a 2 e ghxhmz4-o.0 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, startin9n-0h tvkt k6rxw d+r0g from rest, slides down a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially gij0 nla 7vq( 519lsdxrw7:zlaaven 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 eneee;0 4r dgrpd06d q,f0egctw ;rgy 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 centewe0 dqdc4gp te6g0r ;e;df,0r r of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertifj2 u1pjj(v)nys8/ tho8 -g zhcally upward from the top of a platform with a )n fzjhj-o(pjh 8g81/vsy2tu speed of 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), whosyqs2j2 ew6 3nhe spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it 2s njhwe2 y6q3give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track s,rmm s0j1hw 7/jxz5o gj5oz5zhown in Fig. 6–39. If the block is to remain on the track, even at the jr j75,hz0 j51wox/o szgmmz5top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached tom.26z 1sodrp2zv8qv 6ahj1 rn the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial displaco6 rv1nz.8dr h2ampq2v1js6 zement $x_0$ 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 to ;ei xx*q 1z4psa bungee cord whose unstretched lengthz x*xs1e;p 4qi is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is draggo)f6;ajo/ g8mt c1 bbfed up to point 1 where it is released from rest. Assumi f6 8;jm/1cfatoobb)gng 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 of 12 m/s at an angle oynp- q -,8auaz (l2gryf 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 elevat132yzt4nam5d5ww19uo jy wiqor 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 shoul qzyyw5u mow39d1a ji1t42n5wd 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 cyc xw27fmcxe9t eho;x (-le 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 76u sg5ioqcc91ylw(d v; )n l/6c50 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy is produced in this collisvw1; q69cl5lg( n ousc)dci /yion? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reysu9zvkbn9 1 kd+1j6h aches the bottom with a speed of 2.2m/s How much thermal energy y1nk +huvb d9kzj6s19due to friction was generated in this process?    J

  A ski starts from rest and sc y9y;qkh8/y: fs4h edlides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the gs4qv6p dk3 m o.4vjn1rround.
(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 bac ,p snhi j zh+v04vfp hli21*b.p)yc;mk to a height of 1.5 m. 0p+jblymh s*p,1.;)vnf 4pvzihhc2i
(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 constant cnd2 amxe(a7hiy:q 61horizontal force of 350 N. For the first 15 m the floor is fryi hd (amnc ex2a:17q6ictionless, 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;t zea7 jpr:ahnad0 ej)a- c)+ of If the average force of friction is equal to one-fifth of it0e7tr;)ac jzea+j)-d hn a:p as 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 fo;udcg bw0 id(9ot 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 attac5 cr 12xfsoez4hed to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–springe14oxz rfs5c2 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 the table?   

  A 280-g wood block is firmly attached to a very light horizontal spri)v lokdn;y g (netw4hdlw.17:3be e4ang, 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. Ifk 3gd7bew)l:n ;le he4wta.14vo(ydn 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 includ;0iy 2fim2e qio c6i7aing 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 sq7co6i2i2y i; femia0peed 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 piks*cf+jfji2/,ou7b;/ s fbwz ano to a sixth-story window j2u/fk,* bs;j+7 if/fbsw czo16.0 m above?    s

  If a car generates 18 hp wh)y2ui3emx-k hgv 2 5 ne5l*trfen traveling at a steady 88km/h what must be the average force exerted yeh*nt2)givfk -m uel 52r5x3on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 s. What is tuh4qd30 u,t gzhe average pouut g3z04qd ,hwer delivered by the engine?$\approx$    hp

  (a) Show that one British ho aw4;mqz60qjn9x4qf gc2e;i rrsepower$ \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 expressxc1nt6 tu,g .med 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 that her 1150-kg car slows+2j c j.eyyp i5* qr+e1kzc8sb down from to 65km/h in about 6.0 s on the level when e *s2 iyjqr.8y e+p zkj1bc+c5it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp k /2cn 4gy4tp32dk)zd(ly 4h;pu kr zbmotor 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 motion tak.+ ()v a0rqv k4jroazses 1.5 s, what average power was developed aarvrsvo.kj4 q( )0+z?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.60 m.9 ege k5kiuyi83)ym+h What output rating (watts) shoul3 i+9hmgy)uk8 eie k5yd the pump motor have?    W

  During a workout, the f3 gbfl;)q8ew)t4 w ly)k qpup8ootball players at State U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclwulwptq3f4 )el)8bg ;p kq)8y ined 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 clbfap:u;5ii0 f imb a 6.0 $^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power output of 120 hp. Howhrr r9e aotz3) wgv6*oy9*,wi steep a hill can it climb at a constant speed o)*9rivrtwh wreg, 3 yo9oz 6*af 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor hav2u:yje i9wk zk3kj3yv6;m jl8e to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fr u23:9wk3jz jy6e8 i;lmjvyk kiction is 0.45?    hp

  A bicyclist coasts downuw eev.1b4*idb 7 7zzk/.lup n a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpersxepe2g ;. n6be8n ,xbc7azz(f” that are designed to compress and rebound elastically without any physical dama gaez82ce.6 f7;pnn ,ebx(bzxge 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 by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library the first shelf is 10.0 cm off the ground, and thkn met:/kr) ia4i1 j2te remaining four shelves are each spaced 30.0 cm above the previous one. If the average book ha4km 2)/ejni t1ikt:ra s 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 famous long jump (Fig. 6–42) in the 1936 Olympics show n3ocfv k)dh.0s that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the t f vkh.c3d0n)oop of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in Fi-n r /b: hvn4fik-y6+3ptauqgg. 6–39 is -ybvt/ qg rfhn n6p4+k-a u3i:to remain on the track at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370p t feax575: )rnp*wms5y2ifw m after jumping 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. Assumiym5x:ep fnasfripw) t7 2 *5w5ng 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 okk677zw(*o9n h oa xdnther end is fixed (Fig* 679w 7nhx zo(aokndk. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top n+c2-s wyu3oo(p.1n v ve4fvtwwy 2h 8of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation +wev8-y(.3nvs1p cuw4wot hnv2o2fy of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg l3ek bcz 2ur1p71sm )dhe2vsdye;g 1*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 kx+mmki9q4.-gw/cr f7,000 people per hour. If the average lift carri.f- wxmc i gk/4q+9krmes 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 verticallys4 bfyzhgyx 4*putqu5 7n4-9x 81 m before striking the turbine blades. Cg s 4un4 y4z5q97bfx py-thu*xalculate
(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 so, 4powxsoc- 5h9 gf:with a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circula4 xpgs,9och-w ofos:5r 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 con yh jpc3ot uyudl y1sc,11twf(x)2d+. vert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ) l1ohs c3 + p yj1(tux.c 1ywtyfd2d,)u   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 *w iinl;+)9wtk hj(1vaj 1zltni6e(b 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 batc s8.g t vz0k4qsmajz48f a/1chroom scale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if j. 1/0q4 8 zkavs asgcmzf4t8cyou 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,;4t8kf2wjb ,/7 lor;avpvfmo and swings out over a lake (Fig. 6–45). He releases the rope when his vel;; j8tvol kr7oma/f 4v, fwb2pocity 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 climbspsw) )jx *ieqbumk3s)k1(akzq26 m m- a vertical distance of 5.0 m in 9.0 s. What minimum power xwab m*ms-6(q 3mezp1 s)k ku2j)qi)k output was used to accomplish this feat?    W

  Some electric-power companies use -o+z4uk/uzk+otwu w- water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To store thkz+ tu ou/w-kw ou+4z-e energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constant k is cut in half. What5m7t 7;:ztq apt kz z77oqz *b0ekcm)c is the spring stiffness constant for e0k mz qt5pb7 :77c ot)tza7e ;kqcz*zmach of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a romn0 n 2ic 0f0z 6owucs0rh07kough 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 scf1 5fj0)4pzw mcl.win 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, andfl5zwj)ps1 wm. f0cc4 neglect frictional losses.    s

  In a common test for cardiac functiow t.82yxw,t2w.g g ijon (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the treadmill is sloping yj.ig, x8w .2g towt2wat 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 mp 8pfgz( guy5:, what was its velocity when it left thez8pguy: g5(fp 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 f6/anbhb f 1m/h cykosz6)541 riae3 tlrom a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set upn fak)m6bchyor/l5 ti b 4e 63/11zahs to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s