In what ways is the word “work” as used in everyday languagev;3d y xz/l7we the same as that defined in physics? In what ways is it different? 3z dv/ xlwe7;yGive examples of both.

Can a centripetal force ever do w2vbh :r:xc5ubork on an object? Explain.

Can the normal force on an object ever do wo.d. ei.rb*z n4sro9 kcrk? Explain.

A woman swimming upstream is not moving with respect to the shore. Is she+pr9rmcb ls1d5 lk6* e doing any w6el5r1klds9 c p rmb*+ork? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic frin p* yipbs,e55ction forces always negative? [Hint: Consider what happens b ,5y5p*snpei to the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you are doingmio1s nrxh9yc:,:+/y;pvvgtm-l 4f q no :nfhvsyp/-miy,l14 mqgx ;9t o+cv: rwork?

You have two springs that are :6qipok q3p/q+)n 6w j*zkcauidentical except that spring l is stiffer than spring 2)z k+pcaniw6qup/kq:6o *3q j $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force on e3r9 *wpc bn+2 tln/bga block that is free to slide on a ce3 n/b+*p bln twgr29frictionless surface (Fig.6-30). 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 gravitational potential energy change when p ekr56 c8fewru -*xb;you jump as high -rucf;kp5b8*e w6rxe as you can?

In Fig. 6–31, water balloons are tos(wi 2 oq)kj us+fy3m1dsed from the roof of a building, all with the same speed but with different launch angles. Which one has the highest speed on impact? Ig ( djw)2m+3fqy ks1oiunore air resistance.

A pendulum is launched from a point that is a o7x)jtq 8yd+p:*vdmsheight 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 cause it to swing the xtvso:y)*d+7 q 8dmpjlargest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If yq-mclq;6 v3 yu2pbn v;ou compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, using the law of conservat yq;u23qnl-;pcvbv 6mion of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. xv.vfasw 90ea yhd;1+mb0zw) 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 )x0 9evya fazwsmh 0bd+w1.;vthe ball without pushing it. Why?

What happens to the gravitational potential energy when water at the top ok ,xvf:aww*3/p7ekf pf a waterfall falls to the*ef:7p /vwp ax wk,3kf pool below?

Describe the energy cg,v mi- bplxf(-c5se2 g a9v6transformations when a child hops around on a pogo stick.

Describe the energy transformations that take pz,qv ot+a36zg lace when a skier starts skiing down a hill, but after a time is brought to rest qv +,azt3goz6 by striking a snowdrift.

A child on a sled (total mass m) starts from rest w2lmp 7okrdfkd709f ;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 fwp720dfd9rk7o ;m lkfriction, and (b) there is friction (deep snow)?

Seasoned hikers preferc jrwqtk9 a3q9opd( 0f;sab); to step over a fallen log in their path rather than stepping on top and jumping down on the other side. Explsp 9(fjo )r9a0qqtc;a; dwk3b ain.

Two identical arrows, one with twice the speed of the other, are fiwhq. r;qp pm3l7t1; qsred into a bale of hay. Assuming the hayqt q h7rqps 3wm1l;;.p 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 swi61bii6-akb6a fp*::epuz dunnging pendulum in terms of energy, (a) ignoring friction, and (b) taking frzap6:e:bbpku*nfa 6 u -16idiiction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height grel frh dw(g+2;vater than its original heigg; dw(vr+f 2hlht? Explain.

Suppose you lift a suitcase 5 mvkpf/4fhx, qb9*qbfrom the floor to a table. The work you do on the suitcase depends on which of the following: (a) whether you lift it straight up or along a kx9qp 4*fh/vf5 qbmb, 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 they+llf5hq v1 a62* jy2 xvckq2m work.

Why is it easier to climb a mountaino7y/h9 75 9skljdc.qp1hboq x aaow14 via a zigzag trail than to climb straight u9ay kp.a o d7w/jco9hhxlbq75o 1 sq14p?

Recall from Chapter 4, Example 4–14, that ye4b-ts sk*ql :ou can use a pulley and ropes to 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 for this, using energy concept-tel sb*k4s :qs.

  How much work is done by the gxcrmdq mf)19oi5zwg +z293x v ravitational force when a 265-kg pile driver falls g52xm z9v9wmzodq3c+ rxfi ) 12.80 m?    J

  A 65.0-kg firefighter climbs a f ooxj.o*:slb (light of stairs 20.0 m high. How much work is requj.o(xl*bo: o sired?    J

  A 1300-N crate rests on the floor.tbt. .squ o(u0 How much work is required to move it at constant speed (a) 4.0 m a.uq tt.(b o0uslong 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 cr*;lc7xa72zwx5g sa jg ate 10.3 m across a rough floor without acceleration, if the*w;ax5s c2ajgl xz 7g7 effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by ronjst8zt/0dr(r05wjg1, jx a force across a floor at a rate of for 7.0 s. Find5jjjzgwrt1x, /(r 0r0 n8otsd the net work done on the box.   J

  Eight books, each 4.3 cm thick wlvn*.iutzh6) ith mass 1.7 kg, lie flat on a table. How much work is requirz6i v*lu nt.)hed to stack them one on top of another?    J

A lever such as that shown in Fig. 6-3/j.wb tlhk0 lq,g( r9l5 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of output qhrj0( lbllkgw./ 9, tforce, $F_{\mathrm{O}}$, 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 acceleratisg.)t0mxr2c wng by a man who is pushing back on it parallel to the incline (Fig. 6.gtc)rm 0 wxs2-36). 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 give a helicopte*l0b5o;ndcyzo o 5 ng;r of mass M an acceleration of 0.10 g;on c5 oyb ndlo*z50;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 dis rdohu8sqc+.drza -+d.+ f) ,hg y-vuhtance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown itfu d9g6 ju(4mt np.h(n Fig. 6–37. Determine the work done by tp fgnu6(9tu m.h 4jtd(his 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 ac :mgr66d yuhe(u7 eda2ts 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, a*a k+ un;6ellv/8 qbcan oxygen molecule, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is ddb.0k(ltqf i;cojp5 5hs +iwt7g8 * nuoubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop5kvn:) o rcoe uy6rf in460u1f 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 1zzp:vmuei n2rav+ ;,405km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bowfu:ifvp5, td69 wz:k w 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 as it,vuw: 6 5i:f9dpkfzw t leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s uttp s-.og4 g2f(zk8iglove backward 25 cm when the ball is caught. What was the if-ps4(tg og2uzk8.t average 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 br7gg;;p qik5fe aking distance be increased, assuming all else is the same? Ignore the driv 5g7qkf i;;egper’s reaction time.

  At an accident scene on a level road, investig (p *7x o/yzx,vveu6unators 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 when the driver slammed on (and locked) the brakes. (Why does the car’s mass not mattezoy,pu7euvv (x6/ * xnr?)    m/s

  A softball having a mass of 0.25 kg is pitched at zilr) p6lc s-5 By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance durinlp)-cz 6s5 rlig a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rp+sv quoub,)dx ,u6l /ock go if thrown straight up by someone who does 80.0 J of work on it? Negq,)/ x6vo+dpbulsuu, lect air resistance.    m

  A 285-kg load is lifted 26)e.;gnds0dewac kj: 2.0 m vertically with an acceleration by a single cable. ce:n 6dg)dw ;0a.js keDetermine
(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 stiq1y v.9 :sbi 5 ;a,a13ei b bpqyc;0n;ppluqksffness constant, k, of 440N/m How much must this spring be stretched to store 25 J of :b31pbe; ;.li1 nk5c,qyas0iv qpqysu ; pb9apotential energy?    m

  A 7.0-kg monkey swings fri cnvn5*jk,/h k ,hk7yom one branch to another 1.2 m higher. What is the change in potential energy?y,hk n5 ck/7 vji,kn*h    J

  By how much does the wav :1zolzn( ;gravitational potential energy of a 64-kg pole vaulter change if his center of mass ri(a: wz1 noz;lvses about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whenvlj):hn0 )8t ) vaejv 7tbj+gzv1idv4 it strikes a horizontal coiled spring and is brou vv)7a4)t1jj d lzt: 8b0v)j+ihvge vnght 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 2.20 m ab b9u *bs/ihskemi ji*3 65)vxuove the ground. What is the potential energy of the book relative tohi*xis)b/u*ije m vsb 65 u39k
(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 n* d5.3kkwwh4g 5kh m*)cmnjlm and climbs to the top of a 3300-m hg4 ).*k hc55wk wkm3d*jnnlm 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 v0s rmn(/bne+/ijp-+au ugz o 7ertically next to a 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 end of the spring, where will the end of the spring line up with the ruzmjs rgu/+/( n+o0 nueipa-7bler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs a vine hanzb wikg4+ *6w.su;c :hv kbzh*ging vertically from a tall tre. i c+*w* hbzv:;zusb kwg6h4ke in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a f h 28:dhpw o1;ty8vkeprictionless 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 4bvzkhef9r5 * 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 kinarb t:9x 48zi4vl7d hsetic energy is transformed into gravitational potential energy without v 4x9 r4hdza7st:ib8l 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 cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward 6g mf*qs:fzcq;8y+ dkfrom the top of a platform with a speed of 5.0f+6y d 8 *czgs:mkfqq; 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 rp ( 1vngc,(+p /rwzpkstiffness constant is 950N/m is attached to a tppk(gpc/+n1w , r rv(zable and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown in Fig. y.sf9g: 9zmu yig*-v q6–39. If the v9qi: f* y gmg-zsyu9.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 released?    r

A block of mass m is attached toam0bu kt30x 6iyqbbf ec /*41m the end of a spring (spring stiffness constant k), Fig. 6–40. The block iuamxyi c034mb*bb/ e61t0qf ks 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 b7 f*bl *0zy-4zkqc5lifoq0 sa bridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) lzyz74bo*b qi 5cq0-s * kfl0fCalculate 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 dragks hv jqey++6ex,*fd(ged up to point 1 where it is released from rest. Assv,y(d+*+hs k 6 xeefjquming 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 atzb 0r3wpj;mqmrjb73 ( 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 desigymw ak-vbme:cs1 , yc+mjz :0*ning a spring to be placed at the bottom of an elevator shaft. If the a :cwysjyvzm be c *+-mmk1,:0elevator 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 to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.8 2 hsx4t4d+9 b6kgoxsf$^{\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 travvldo.f;r8 6i/ m4lmuteling 95km/h in opposite directions, colli46dt8lmrl; /.fi ou vmde head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and reaches the 30g fjhst9+(rgotw;rbottom with a speed of0s+9h(tgr wf;orj g3t 2.2m/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slides d1 byn;5ff;ze7q ref.cbbdz y cq5g8)9own 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 theoi9cd8eam*f,ht e- 3 c ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height of 1.5 nmbjy6o0.b6ugin 2 m9 0 wyp3im. 66ibj 9b.y3w2i 0gynpuo mm0n
(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 rvlian(cirlarl95l1hl 63 q,9 est, is pulled across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of frictio c5iva r9 r qa3il,6l1hn9l(lln is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–tq* /rn3vq2c b41 passes point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, witrq2c/q*n b3 vth what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches2zwd 3:kc71s bh7 vs l3ah+swr the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood blocv+o i ug,et++l l7z/m+zyq m*ik is firmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, le+itoq +zym,g+*mluzi7 + /vwhen 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 horizontngyyud yb2b5n:-* 0cn al spring, Fig. 6–40. The block can slide along a byc2:5nyn u*-y0bg ndtable 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 swing?    m

  Early test flights for the space shut4a1 xsup ao )qavz.js9tb7*x,zh-o57 u ob7nbtle used a “glider” (mass of 980 kg including pilot) that was launched hat-71s oa*s. ,z o74xxbu9pz7hvjun 5 bq)aob orizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano to a sixth-stt:pwol,m5 q1u rwe --uory window 16.0 m ab5oerqm,1u-l wtup: -w ove?    s

  If a car generates 18 hp when traveling at a steady 88km/h wht6;byaa 5vrq/ md0pi: voge; 9at must be the average force exerteiv6aqm/5v;b g a d:o;y0pt9erd on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest r 92q 9hvk1 iz unk9y6n2p/iqx*9xulhto 95km/h in 7.4 s. What is the average power delive huixik*296h2 91q p n/ vznyxruq9l9kred by the engine?$\approx$    hp

  (a) Show that one Briu3 f :odk2l;nxtish 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 “kilowatt-hours.”m4g8u (5ya jhu
(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 8tm+ kw:;+jdtmum g( 8rul7ts slows down from to 65km/h in about 6.0 s on the level when it is in neutral.; mt r8dl(7uk:8+ sjwmttu mg+ 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 motor do egz-gdtrv f,*;n,cud 0 r o7x7k z,tt6in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to j.gwmx6 ec 93l14m/s If this motion takes 1.5 s, mcg.lj 6ex3w9what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minut xl7x:tkp7 6hdppjjd5uc - 3j:e through a height of 3.60 m. What output rating (wattdp lt 77dj p:x5 :3xhujp6jk-cs) should the pump motor have?    W

  During a workout, the football players at State U. ran up the sngchr3, ei3x6 tadium stairs in 66 s. The stairs are 140 m long a,rexhcgn i 363nd 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 6kfm:u rr qmj80;.sgd;.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 ( +q rxqj5zsusoxofnb 6, y2*-steep a hill can it climb at a constanuxs,26r os5-o*yq( fzxbj q+ nt 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 drag a 310-kg box along t+0,c50 lenpcki/ p dpa level floor at a speed of 1.2m/s if the coefficient of friction is 0/,c d5n+c0pitpp kle0 .45?    hp

  A bicyclist coasts dx y1 rn6m(at4yown 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 )7 ik cu52r8c0e6.uylwgi.wqq3nzst/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 thuucn 78 eg3ti) yl kc 0wqz.r6.5siqw2e 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 groun+hs otr5 ob+;qd, 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,s+h;t 5rbqo +o 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 shoj(hioiz;,x *t*c qi m3q,/c a) zc7arzws that his center of mass rose 1.1 m from launch point to thei x)7*/zc hi*(t3,za;icz ca jomrq,q top of the arc. What minimum speed did he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction along the looped track showniyht: b(y)n3y ) u47anot0ssk in Fig. 6–39 io 0u4( )yyi:73t)s nthbnsayk s 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 370 m after jumping from an aircraft without ha7 c7vbkf10 m;n p jripdg.d3-is parachute n7 r d mk ;cai-03djbpvpf.7g1opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his 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 otpm2coopf 8w)mf.j84 dher end is fixed (Fig. 6–43o 2f m8 dj.wp4cf8)mop).
(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. The climb is made inp faq1:ul1a hoy (0no) 5.0 h starting at an elevation of 2300 m. Calculathao1(uf)aqnp 0:ly1oe
(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 hsd5/uyd 4tbyk6( krmxn7x xa9 y71j,f uge 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 (l5jn p-)h:6-bs emg5e xnqm kmove 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, e5nhn:g-bpm mxqks 5lej( e)6 -stimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at thep* tps-aq+ 0ky rate of 650kg/s and falls vertically 81 m before striking +*p sqy ta-p0kthe turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circuldz 5xmc.18 dekar vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular lo xcm8.ddkz5e1 op 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 coud4)6 vrm7fy;y0scoy rld convert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled s)v4c oy;7 ryrd 0mfy6by 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 an7kfgbz. x;r f8dk2zg0gle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compresses 0.y1r8yspqkq do 15+5am60 mm, and it tells you your weight is 710 N. Now if you jump on thesqy 1ak1qor d m+p58y5 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 grabsn9,kxd )e6r sq a rope, and swings out over a lake (Fig. 6–45). He releases the rope whene s krd9)x6n,q 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 a4zrxi(5w yhk v7j:;id vertical distance of 5.0 m in 9.0 s. What minimum power output was usedh; i5w(kyjid: xrv7z4 to accomplish this feat?    W

  Some electric-power companies use water to store enbj(mvad 3*.z cdlj4yz: oh-4cergy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To stj34vlo(byjc.d :*cd z zhma-4 ore 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 stiffnxex l/eqy89 ;ness constant k is cut in half. What is the spring stiffness constant for each of the twoexlxq8/y e9;n resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up a roug exmjbz9ey/ 5d56 w3yjh 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 3.3e*gd- e1d8o:b0 t rup ogrve+da(w m)2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neug38e1gbd+to0(moa pv- d)er: rd*we glect frictional losses.    s

  In a common test for cardiac function (the “stress testwct:s;8by e3v”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when ye :t c;8vwsb3the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock vertically upward a distance of 500 m, wpp:2 xx; 5d-ucde6fd+few3 r hhat was its velocity whe-ed du;2f3x6 5wf hx r+p:cdpen it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel xunnoq;: yy4q 4:ll/ pfrom a height of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electxlyln:4o4uq: pyn;q /ricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s