In what ways is the word “work” as used in everyday language thlh gat:m:rt23e same as that defined in physics?gtl ::23armth In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an objectt wsnvbr 0ckd7bsx3xl r8, 125? Explain.

Can the normal force on an object ever do work(cbngr1 h9k *h? Explain.

A woman swimming upstream is not moving with respect to asxt1 1t6o .pxthe shore. Is she doing any work? If she stops a.xp1tx1st o6swimming and merely floats, is work done on her?

Is the work done by kinetic fris 2vg8 5s.xgldction forces always negative? [Hint: Consider what happens to the dvxgs5 d l8g.s2ishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wr4t1bblca426l vx,huall even though you are doing no work42 r4b6, 1bvlcl hxtua?

You have two springs that are 9/apf)9s6i r nqwfn)k identical except that spring l is stiffer than sprr9sfq )k a p9)fwn/i6ning 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 to slide onwyt/ts:r:l * r a frictionless surface (Fig.6-30). The block starts from rest at þoint A,/slr:yrt* :wt 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 chan0ptxra, p)5y uge when you ju5)ra xpty p,u0mp as high as you can?

In Fig. 6–31, water balloons are tossed from the roof 6hinfjz1 hk9e g;hn+7of a building, all with the same speed but with different launch angles. Whihiezhh7f +6j ; k91gnnch one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is aa ;5zl //uxz y:6qkxni height h above its lowest point in two different ways (6a/uy;l/i5n zzkxqx :Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on a table. If you compress the sp ) va1+(tl*u9w puwntjring by pressing down with your haj(ul9*)tv ua wn1p+wt nd and then release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceiling by a steel wire (Fig. 6–33). The inanhl,;c6fuc 7structor pulls the ball back and stands against the wall with the ball agai cu,a6f hcl;n7nst his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy w zxl z5o-qe;utkr 9kxt *-- e5zft3m3yhen water at the top of a waterfa t5z t zmy;3- 3toxe5re-l z*x-9kqukfll falls to the pool below?

Describe the energy transformations when a child hops around onzd 3(d*ws jgsl cs-9/n a pogo stick.

Describe the energy transformationl rs8ibtuvuaje:4l8( 4 ex (9bs that take place when a skier starts skiing down a hill, but after a time is brought to rest by (e ue4ai84x r9l ujbs( tl8bv:striking a snowdrift.

A child on a sled (totaldj 6j+ril j.)q mass m) starts 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 fricjrd6 .ljq ij+)tion, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path ratherv csocbt *c *vku:(c)/ than stepping on to: *c/ cu*vbsk (tc)vcop and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of the other, are fw wbg7aiv0*ctv50 jna;hp.: bired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther than the slower arro05 bj ;vgbwtac7p .:*hvwna0i w? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy,gx 9rkh 5: sxuhl8.iv1 (a) ignoring friction, and (b) taking friction into account. Exp9s: u.i1 gxxvh5krl h8lain why a grandfather clock has to be wound up.

When a “superball” is ayu4lo9*34dv 53;-rcync uuwr uwu;jdropped, can it rebound to a height greater than its original height? Explain5rwn ;u3;cv 4yr*4wcy9 u ju-uudla3o.

Suppose you lift a suitcase from the floor to a table. The work6 fth98jx +mr61s2btp9syi 0kds-p eh you do on the suitcase depends ys1e9j6khxhtp r i062fssm d p89b+-ton which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the powzuq du+ bf*pv bz.4hdp 8rr413er needed rather than the work.

Why is it easier to climb a mounj(0t7n xp)x0 tft4g kwvd-jghz29(f r tain via a zigzag trail than to climb straight u9fkf d)p w2 0r7zt (g(jxn4g htx-0vtjp?

Recall from Chapter 4, Example 4–14, t1vwuwq1)5y lo hat you can use a pulley and ropes to decrease the force needed to raise a heavy load (sewwvq u511oyl) e Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driveozjc 8( ;,9 qgq9zl5en2jhyf sr fallsjsl qh;(5y 9fj 2 o,8gn9zezcq 2.80 m?    J

  A 65.0-kg firefighter clim9u x zb;*uc1wrbs a flight of stairs 20.0 m high. How much work is requx *b1 9rwucz;uired?    J

  A 1300-N crate rests on the floor. How much work is required to mdu*;it aesy6iq8-d yo+1m7+m o fh8jz u(pb5fove it at constant speed (a) 4.0 m along the floor against a f6u8bdo*1ii+z7t fu hs( 5q+yyp fo8m;mdj-eariction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did th mi+u/5t sh3 d/hwzl3be movers do (horizontally) pushing a 160-kg crate 10.3 m across a rough floor widz533 /+ ihhmultbw/sthout acceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force acfz1v71 9rdk jyles31 7 s/gkm;l7r eyxross a floor at a rate of for 7.0 s 713jl17m/dys vzke rglxy;9 fe7krs1. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. 12t4; 6lsgw os8let krHow much work is required to stack them oneweo2 l41r;stskt8 lg 6 on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff obje ,9 tvw-u b6kxqj0zy3tcts we might not otherwiqwy0,-bz 6t vjk3xt u9se be 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 dow0+.ckjv2u,oi sc 3wx.em;x tnn a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.x wuk+i ,;..jn0cv o2sx3ec tm40. 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 helicopter of mass M an accelqgi1( 9 fjj fkfv)7bd:eration of 0.10 g kffdfv jbig 7(j9: )q1upward.    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 distannq1tl 6hlh 4o:ce 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 shownxqil* v5t( fy g*y5.+ vx0svtq in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to xv(gsx*v +l5f0 5t*vxiy.qy qt = 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 on6ht dmoe ;174t srhj,.xled1 b 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 molecu(-k1-hpdv jwzbkww(k(k i: v)q; a2dale, with mass of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doubled, by what factor h y/ x9h cp-qqja1,djsnnv7rvxk.+u2i*n)4atas its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop ut:pxr0/3c1 -boh u o5x1xw c 7i4somian 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-kgentslg,) 6) wxcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose+ir idn4h6:qd string exerts an average force of 110 N on thh+d6i 4nrid q:e arrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) travelingshd5 *q ygqx3 2kky)t9wdpt3opfi.;3 32m/s moves a fielder’s glove backward 25 cm when the ball is cx tdfqphk.5ti* odwpk33 q29y )g3sy;aught. What was the 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 braig qp46 v*gx:8w6hijjking distaniwg i 6h8p*vj6x: jgq4ce be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, inves aue8)k.6v 7ftq- mapmtigators measure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic 76 tpf va-qmm8u. e)kafriction 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 off7h c:l(rq-9crr1p gd 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Negle f g-:cqd(7rrhrlc91pcting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock go if thrown 7hujpb dc9 l*+straight up by someone who does 80.0 J of wo7u 9pjl b+h*cdrk on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration 1 nm1i+my5ytns2j0k4bw i2 xp jf (ei0 by a single cable. Determis2jmpyeifn2 jn1 5 t41 iikb0 +x(ywm0ne
(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 constant, k, of 446 bnl32piouo:co v o9,0N/m How much must this spring be stretched t2ipnbvouol o :6o3c 9,o store 25 J of potential energy?    m

  A 7.0-kg monkey swings from on+0+etc :)8lntn umbia e branch to another 1.2 m higher. What is the change in potentialnct8+ln b0i+ut)m: ae energy?    J

  By how much does the gravitational potential energy of a 6h9llm,xc k 1v04-kg pole vaulter change if his center of mass rises about lx90lchv , 1mk4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it strcc*0 y aco4gsm-uhem1rv2 m kwe :i/42ikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. Wha1g4e mwaukcemir2 s 0mv */y2-c :ch4ot is the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person h uf rykn-6 -xh;qlh9on2*)qxlifts a 2.10-kg book from the ground so it is 2.20 m above the ground. What u h-y2)kqnho96 -;nxxr fhql*is the potential energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs to the top of a 330ns- wxk 25iv9w(ehkt0( +uhktt.; gnn0-m peak. ;-t 5.( wh i2ukghs wn09kn+nk(tevxt
(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 ( 50:pfvjxce nhangs vertically 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 ruler marks?n5jxfcep0v ( :    cm

  Jane, looking for Tarzan, is running at top speed (5.3 gk)6jy vr9vt;m/s) and grabs a vine hanging vertically from a tat6)r9 vj v;gykll tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides downqu:dk hu.aao2 u6 8+dz a frictionless 35.0$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove d9m dpy bt+ ,4q.+ygatup a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s kinetic energy is transformed into gravijgxq;4,j indetlr0 h)bp 9r 7:tational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and c) gt errb:;qh07j4l9njxi, pdross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the tz2yc i dd-;w;iop of a platform with a speeidy;wd2z -c i;d 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), whose tqe.9e0f3oa ; nh:hnjspring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 mh:n 0.3fqjn te9aeho ;. (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 Fokf/8w v : nbgmb.0hx;2l4nl c3dyo 9mig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what4lmclnkfb0 .:bo; d8v hym/o n9 wgx32 minimum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stiffness cons3s;fj2 -rgoa c/ b)f.mu brw0mtant k), Fig. 6–;.f- mmb gw2ab 3j/urrfo0 c)s40. The block is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied to a bungee cord whot0efuw +j.+rk(7a tixm b g(3cse unstretched length is 12 m, and falls a total of 31 m. (a). fkgi7wrx3u(eb(t 0++jc tam 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 r /oihfi4 h +*b+ fti-8un;miqshown in Fig. 6–41 is dragged up to point 1 where it is released from rest. Afqi mobh+ i4fu-n8;hti / r*+issuming 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/,d 2ixwrpgpw9l5, :6bnvt +w zs at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at the bottom of an .cbp+/7o wiobelevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest.iwoc+ob/ .7 bp Let M be the total mass of the elevator and passengers.

  A cyclist intends to cycle up a 7.8 g()k(iu +yeri $^{\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 of7 fo-9kcuuf 6u mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. How much thermal energy7 fou9c6-fuku is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends a slide 3.5 m high and r h,6,0sacbtki rtv pl5-,:ldqeaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was generated in this proc:,,klviahd0l 5qr s tb,c6tp-ess?    J

  A ski starts from rest and slides don:(8k yovyjiw0* q5wxwn 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 5f(xlvjin3 x*hjna5 .e:)ymf tree 13.0 m above the 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 5lkt9osk 25f dheight of 2.0 m, and it bounces back to a height of 1.5 m. 9fd55ktsl ok2
(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 apk3sam8 f7fn 9 floor with a constant horizontal force of 350 N. For the first 15 79fk3m asn 8pfm the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a speea1 2hjk*;bv5*jenu ;/ f0zbpl jiqpp, d of If the average force of friction is equal to one-fifth of its weight, witp01 ej bi;kf2 azpv*nj*;q,j hbu/l5 ph what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 126 a/ xmmpu;d-x7rg7ir/t 6 daxm/s reaches the foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring (k=1bkh2 weaoo5kg,a++uo - 9rj,o80N/m) as shown wb2hg,ke ,j+u 5a-k o+9ooroa 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 the table?   

  A 280-g wood block is firmly attached to a very light x 7)w ybmd6;xruda+w,horizontal spring, Fig. 6–40. The blodbx7+drwa; 6)xumy,wck can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights foq7b nj/6v bk4fr the space shuttle used a “glider” (mass of 980 kg including pilot) that was launched7fqkj b/vnb46 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 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 (huk7h+ 9pxp fmotor to lift a 315-kg piano to a sixth-story window 16.0 xh(h p79up +fkm above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what must be the av7j) ohax, uk:kerage force exerted on the car due to friction :7x a)kojhuk,and air resistance?    N

  A 1400-kg sports car accele:voq +tjz+gft) 4c e6trates from rest to 95km/h in 7.4 s. What is the averaetto 4fj c:+q t6z+v)gge power delivered by the engine?$\approx$    hp

  (a) Show that one Britishq-l2ey.ud0w+h;7 taod 5f6boyr jxo; 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-ho+s 63 zkp sfip3;gqi+zurs.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about 6.nom sz;imkh kodyqat9 k)z dwo:7,,;hvx6((40 s on the level when it is ino9wz7 t onk(ami,dmoz y;x;q khs v:),6d h(k4 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 m koqu33cd;gs4 c4cl km,:.xwhotor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot fro9 8x pzay+8owcm rest to 14m/s If this motion takes 1.5 s, what average power was devel8wp8ca+oyz9x oped?$\approx$    W

  A pump is to lift 18.0 kg of waterpu80 (nm 5ja9cfph s(t;xvw*+:edvp c per minute through a height of 3.60 m. What output rating (watts) should tt(v cpepmncfx *ha v 9p5s;(0+wu j8:dhe pump motor have?    W

  During a workout, the football players at State U./7ydwu u- v sbwb7b++l ran up the stadium stairs in 66 s. The stairs are 140 m longubl7y7uws w/db-+v +b 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 l1 ot6v+kff:j pf;;x bclimb 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. How steep a hill can it climok8k +58fmhnxp*)v hb b at a constant speed of 75km/h if the frictionk+ o5 mx*fkpb) hvn88hal forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have *+x/t nrz1mrx to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fricnt+/*z mrx1x rtion is 0.45?    hp

  A bicyclist coasts down a xx s:bnum;(o)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 *h,bfki;4g vv,t3d pp have built “5mi/h(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 ctp,, ;fvh4 p3v*idb gkonstant 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,4/ q zg2trz:f0.pkff z and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average zp.z t qr:0f24zgfk/ fshelf 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 srzw7 r3ir ,:bf2vij 1ghows that his center of mass rose 1.1 m from la1 iirgf7:vb ,r2wrz j3unch 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 top of the arc?   m/s

  The block of mass m sliding without ao-oze kg91y3 friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very toygoz1k a3e-o9 p 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 afterztr-knhe6. q05ny x,k jumping from an aircraft without his parachute opening. He landed in a snowbank, creatrxz,.he6n5 kq0ky-n ting 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 cop 2n q3zr *kvnv cwbw1n09m9w;ival.5rd of length L whose other end is fixed (Fig. 3 .na *9wn9r 5iv1bwq02nvmzkw lp;v c6–43).
(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 of a 3700-m-higx:sl x 49lm3sa- vihsd39ly.vh mountain. The climb is made in 5.0 h starting at an elevation of 23shv.i: x4 l3s ls9ly-advm 39x00 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28r*6 :u anuob/*6lp 1i cfse-gravb3d. 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 th( qq3i whthzj .:obdrmz5j(-5at its lifts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, esmw-oqr jz :hh (z5.j q3(ibd5ttimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls gj)j8.ipqp,wxa u tzjh. 80f* vertically 81 m before striking the t0pix) ut .aw,f.j*pz 8jqhgj8 urbine 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 wiq v0 spkmf* n5h5zf-c5th a circular vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottokhfc0p f z-ms55*5nqvm 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 candy bar directly into work, how high cou5y/m98mbna r,j (i1e mlium/f ld an 82-kg mf li8euj b(i n,mm5a/9/1r myman 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 anq xq7uff3xl o7g5a-)+brkd8 c upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scup3 gqcjw16 awz.2wg1ale, the spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale fwgq u2w.p wajc131gz6 rom a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swro:ib t/-rm;wings out over a lake (Fig. 6–45). He re:ow-r ;btrim /leases 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 distance of 5.0 m in*j 1pfsvr+j jl1tdfz )z-6cp / 9.0 s. What minimum power output was used to accomplish this feac f+*t p1p)z6sf jdj/z- vjlr1t?    W

  Some electric-power companies use waterywsksa- ei gd8 g7rew4v67 kn/9k5,ul to store energy. Water is pumped by rever9yrawud e4gwnkk/,-esg li7 65ksv7 8sible turbine pumps from a low to a high reservoir. To store the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffnessi fn) qb(o:u4j constant k is cut in half. What is the spring stiffness constant for each of the tw4:of qb(i j)uno resulting springs?   k

  A 6.0-kg block is pushed 8.0 m xhf -.m-wcwd0s).ad lk5 j*goup 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 acceled0vq l/lg tp/, t0 -:;sozkknr7a 5imkrate from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55kk0o;:g,l vkrsta qt /-n57dl0i mzpk/ m/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for car6xn amvr:(v e9diac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power rv( me9:vx6ranequired from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a c9uog( .v8 n1/gefpi m500-kg rock vertically upward a distance of 500 m, what was its velocity when it left the volc(.g 9 vmnfu/1pi 8cogeano? $\approx$    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 h oe.;7l+fs:d gen6u z3lihl* leight of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to pr u;f l 3d.i ln7l*sz:o6h+geleovide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s