In what ways is the word “work” prm+xee p(a2dmh91dtq5 . y,itn-z n+as used in everyday language the same as that defined in physicpye.ah5 d,ep(1+zi-+t2dtnm9n qmxrs? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an object? Explawq v vhpkgxt51su15(: in.

Can the normal force on an object ever dojh 7jht/60 mvypdk.8pd o04zg work? Explain.

A woman swimming upstream is not moving wibl6gx7/1 vtbj th respect to the shore. Is she doing any work? If she stg vjl67/b1b xtops swimming and merely floats, is work done on her?

Is the work done by kallqi ft 586oqn+0 o: v6s4yvfinetic friction forces always negative? [Hint: Consider what happens to the dishes when you pull ai v8yl056:qq4t6favn lofso+ tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you ar4o( uwmde) +bde doing no wdmweu do(b)+4 ork?

You have two springs that are identical except that spring ldnc6 zc: zfrwb-oa dx6/7nj:p,dk0 5p is stiffer than spricb-6z,7 :nnfwdj/6 adzkdp:cp0rx5o ng 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 horizontahjgfn);jk( 4u l force on a block that is free to slide on a frictionless surface (Fig.6-30). The block sta;f4 jukngh)j (rts 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 0;q(ndv7kj hfchange when you jump as high as you ca v7d;n(fjh0kqn?

In Fig. 6–31, water balloons are tossed from the ro p:/e-wl)tu9fgzsg2cdpn (; . dmtnd 8of of a building, all with the same speed but with different launch angles. Whl(dp;:8dnw9g. f2zus/c n)tptg emd-ich one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height7 1 ckqx fj4)ezxw0on0 h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is gix0je)ncko 1zqxfw074ven 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 spr*fa(oa p )*orbing by pressing down with your hand and thenf( bo*)aaro* p release it, can the spring leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the ceilifjo.k8.l)l0hancdk ; ng by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against tho 8ln ;jl)..hkcdak0 fe wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational pov7a8w zpo6 lq;is*:tstential energy when water at the top of a waterfall f o7s ;waqvt:p* l86zsialls to the pool below?

Describe the energy transformations when a child hops around on a pog0mbjji( n2 yb8f;izq5o stick.

Describe the energy transformations that take place wh vnuph9ma .8dt fu*)+sen a skier starts skiing down a hill, but after a time 9pvus)8 .h*futdm+anis brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest q ;v+0mj+ xmnzr e.qb+at the top of a hill of height jqx n r.0q +;mvzb+m+eh 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 (b) there is friction (deep snow)?

Seasoned hikers prefer to q l5w-i7u+v *mot*zvystep over a fallen log in their path rather than stepping on top and jumping down on t ivu-*twvy zml+ q57*ohe other side. Explain.

Two identical arrows, one with twice the sdrmv3/ae r y9*(p r3sopeed of the other, are fired into a bale of hay. Assuming the hay exerts a constant frictional force on the arrows, the faster arrow will penetrate how much farther thayrpav*e/omr3 rds3 ( 9n the slower arrow? Explain.

Analyze the motion of a simple swinging pendulum in 7+tu0otb (ivvab1)h t terms of energy, (a) ignoring friction, and (b) taking friction into account. E +(ab) tih 1ovbvtt70uxplain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height greater than its origi1ajcm)wyat 6bd3,ad1nal heig1yawdb31t,ad a 6c j)mht? Explain.

Suppose you lift a suitcase from the floor to a m 1o;dx ;lmzz3table. The work you do on the suitcase depen;xl;oz3zm dm 1ds on 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 x w pj:rk4(ch-power needed rather than the work.

Why is it easier to climb a myyx +/b :wyw4x1 l4bnmc8sr( eountain via a zigzag trail than to climb straight unx:wx8 yl mrs44bw/1e y+ b(ycp?

Recall from Chapter 4, Example 4–14, that yop -nn8rq4fvqn .xu:2 ju 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:nq.nx4rf n u2qj 8p-v be pulled up? Account for this, using energy concepts.

  How much work is done by the graviyr4gk7+-mzo*zv g t,w tational force when a 265-kg pile driver fallsvzk gr t-7*o,wmg 4+zy 2.80 m?    J

  A 65.0-kg firefighter climbs a flighfi2l se,c 9wqig9 cc36t of stairs 20.0 m high. How much work is required?ci,g93i9flw sec q62 c    J

  A 1300-N crate rests on the floor. How much work is required 2 l a)6pc)zmb 6)cfs *dsy5puito move it at constant speed (a) 4.0 m alobzipsm fc6du* )2a5)sp6 cl)yng 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) ws2x.j o ya-q1pushing a 160-kg crate 10.3 m across a rough floor without acceles.oxj21 - qyawration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a fu.56skbq5a ) ekj yq8iorce across a floor at a rate of for 7.0 .s yib6k5uj5qekq 8)a s. Find the net work done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie fl8be9xk (*pc3 h hr/itfat on a table. How much work is required to stack theref k3b*(pc it8hhx9 /m one on top of another?    J

A lever such as that shjw+iaph4mln(4p4c5 x+g m 7ha own in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Sh ++ a4pch( 7wnxlhgj5ip4mam4ow that the ratio of output force, $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m down a 28° il3+ob+d ljup* ncline 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 ld uol j+3pb+*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 helicopter of mass M an haabbbme1io +- co+++acceleration of 0.10 g upab1 b-imo+h +e+oab +cward.    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 dixckz5n l,9 om1yvy05qe- ssd3stance 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 axc4v/emco8plx jl0: ,dis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from x=0 m to x = 10 md0,ej ml l4xo/8v: pcc    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 p/q88z0y m6koh xggni6 article acts in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mass of9 90 wdz;oldfj $5.31\times10^{-26}$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 arw03, nmes7: ch. ukcaarow is doubled, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to stop an elecwubk2va 60q nu dyhu6+9 jy/:zvahk*3tron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ 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 bep.s zd/k 3rs0t done to stop a 1250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow w4k*fu 7l,xwy .r xr+yohose string exerts an average force of 110 N on the ao+ 4,*xkw7 xfryrluy. rrow over a distance of 78 cm. What is the speed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 c 7oty89mxv t:om when the ball is oo7 :t mv9txy8caught. 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 minimu9.2sbg2jt 7y0j zh +euaq83fdjjv p.t mf6;blm braking distance be increased, assuming all dgj26yf.tsuj3;bv h f07 p t2lqez a9m8jbj.+else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators y xi3tt28 2hwnr3yjo)/uf 3mkmeasure a car’s skid mark to be 88 m long. The accident occurred on a rainy day, and the coefficieyrt8)i nok/ 3 htw2uj2ymx3 f3nt 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 c(:6l . nf,*mh(vhwzxp+k iuekg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance6mf(zu,n : w.*xi(kpvl ce+hh 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 straight up by so(of;k) k-u2 a8bsaq8 m3ymuaumeone who does 80.0 J of work on it? Neglect air resisb k(3a288mq-sya;uoauku )m ftance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration . (*mnash fv1vby a single cablv fh.1vmsn(a *e. Determine
(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, o(,ffl tgrahx:c-ck y j42l:e2f 440N/m How much must this spring k2lextj:- :lfar,(gyfc2h4 cbe stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from o9bp b0 n-fsr2sne branch to another 1.2 m higher. What is the change in posr09fn2-b psbtential energy?    J

  By how much does the gravitational b9myvdqa +g 66m,pz(w potential energy of a 64-kg pole vaulter change if his center of mass rises about 4.0 m durdb6mp+(qa 6 vw9y zmg,ing the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it str 6b71(n2oxore8vx ul7tlm 5vfikes a horizontal coiled spring and is brouv5(8lf nbo tr7x7x6o1uvel2 m ght 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 b4+/zlae ag 3lit is 2.20 m above the ground. What is the potential e+el43 g/balaz nergy 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 330dvs0nj7 sjvuv4w. .1ym;ax r32 oris-0-m peakm d.uav.r vsy7oxr0;vsi4jsn2 13j-w .
(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 = 53Nn6z8fh - urye4l2c2bkim-j u d 6-4o;sjqm-xn/m hangs 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 sdk4 by4- -jc e8 -u6m2oznujhs-;6milrxnq2fpring line up with the ruler marks?    cm

  Jane, looking for Tarzaj.gbj;mond jid es+0a +0m1q 9n, is running at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward? + bnd +jd gsq090;e1 jmmaj.oi   m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting frf v/5 zx o.1kg noc2j.98ueazoom 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 given a shmz+notl/mwfdrx .h * 6*x-bd2ove 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 energy is transformed ,goo * *mois0i*wg uo(into gravitational potential energy without the aid of a pole. With (**ou,io* wg0osg omiwhat 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 upwardzg8 l2inh2 o9p from the top of a platform witn92 zhli2o8 gph a 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), whose spring stiffness constant iska(epf yq1 f*b) va)6n 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when releq6vfkea(p f1)by n)a *ased?    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 tra c8ssxcpc5s moo z9+70ck shown in Fig. 6–39. If the block is to remain on the track, even at the top of the circle (whose radius is r), from what minix+ s ocos9s7pmcz08c5mum height h must it be released?    r

A block of mass m is attached to the end of a spring (spring stis h-js) +4: z/pyidhoyffness constant k), Fig. 6–40. The block is given an initial displacempzdh)ys/o - 4si+h :yjent $x_0$ 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 bd )qhq1hee+)v +p xqb2ridge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the sprve2he1+ qpx))b q d+hqing 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 dragged up to point 1 where it is ryl2(9kir;uzw c7g 2k beleased from rest. Assuming no friction, calc7cwybz kui2l; (29rgkulate the speed at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is throwof3o6u+)x jsviyb y;2 n with a speed of 12 m/s at an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a spring to be placed at th,9k(tl7t yt (gxfkiv3ll.. dfe bottom of an elevator shaft. If the elevator cable should break when the elef f 7tlv3it lgdxl(k,.y9t.k(vator 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 7af.yp:gdh2 4 n7wg 8ct.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kzp8su lt )ao0 hmv9g5 4/w3;gm4f vtvxg and traveling 95km/h in opposite directions, c9x; 3v) z /5g0s vot8fm tuamwpgl44hvollide 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 bottom witsw)18 pjjf:xnh a speed of 2.2m/s How much thermal energy due to friction was generap: xw1j)fn8js ted in this process?    J

  A ski starts from rest and slides down a + /4af 1,wkieuopbjb/ 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 t-0ae 9tppj *- ynqkxu,8ypj l+he 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, anngeg 1n;2oqu 5rc7(wdd it bounces back to a height of 1.5 mgw5r2ocnqd u 1(ge7 ;n.
(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 ,o*n9eju7d:frr2r 1wxuba r0with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the n r9d 7rfubonrae0w *:r2u,j1x ext 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 paskm; 0mx;nvmw0 ses point 1 with a speed of If the average force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The0kx;0n vmm;wm distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot ofmrmq)2 r/v(3jkvfs h - 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 fi/yt po51 (l2iq con+ed5e3qml rmly attached to a very light horizontal spring (k=180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches ouqt2o lp5mee5cl/d1qi n 3 +(yot 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 dwyh:p5d*le 6l0rw q(4s3ovdvery light horizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch h( ydo4w 0:wd*65r 3vpsldleqon its first swing?    m

  Early test flights for -y w tmyh1v,gg;8t6gxwkg d*n ub)4*dthe space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/hy4bntm*t8vkd*g 6 w hg-y dg;1ug,x)w (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 lifq;ir6;oyc,r a60;litgr db*r t a 315-kg piano to a sixth-story window 16.0r;;y a6i6,rl*io dtb gqr0r;c m above?    s

  If a car generates 18 hp when traveling at a steady 88km/h what musl d2d,d3;hbws ho1/lkt be the average food31hhkd2;ld/ lb w, srce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4 hu8kgogp3 0nz) hdh89 s. What is the average power delivered bg)nkhdzup 8903ohg h8y the engine?$\approx$    hp

  (a) Show that one Britishxg8czv) )chdg *y2h,x 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.”ke fw*i(ya /)9hi 5gxv
(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 fl 03 .qwgmdrf0:e(fw to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car trave0e (fw 0fg:dflrw .qm3ling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 5 ;r2c/z+is/ tklnz jmri6vc-1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3*f3jj lfajy, *-kg shot from rest to 14m/s If this motion takes 1.5 s, what average power was d*3fjja fly,*j eveloped?$\approx$    W

  A pump is to lift 18.0 kg of watxx0dbdokhre6l ;: r(q/xp+8 wer per minute through a height of 3.60 m. What output rati wlo8r 0bxphrd/ +x :;x(kqd6eng (watts) should the pump motor have?    W

  During a workout, the football players at State U. ran up ;mqvzs():s v hthe stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle sv):svz;mqh( 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 clim4. (nfbkik e5jb 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 maximumee0ismptt-aush(pn+s- w;ux 11 81gj power output of 120 hp. How steep a hill can it climb at as x- 1eti0uwna8sh1-;1 p( jepusm t+g constant speed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor hav 15wu9f d0 2shuj2 wo-2dlfotde to be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.420fs5o t19 udofduw-wl22dj h5?    hp

  A bicyclist coasts d7m oujili mf /z29g9z8own 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 bx;b0px wxly)r ,c7j. ouilt “5mi/h(8km/h) bumpers” that are designed to compress xj;w.p o,7lyxxrbc0) and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the 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 the remaininw o3lf1d 7gua2g four shelves are each spaced 30.0 cm above the previous one.wf2dguoa317 l If the average book has 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 Olk6 a(l g)nw,p:xybg/nympics shows 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 then/yg 6ka )pb,(ngx wl: top of the arc?   m/s

  The block of mass m sliding without friction along the looped track shown in Fil h2(0zvx ,nl 1: gj5.y:x qo8gwqxmgpg. 6–39 is to remain on the track at all times, even at the ve.gx(5 0 qxxjqn1vhgm:go ,yl:w lz 8p2ry 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 his par ng.ycupg)xpy4o(7f9 achute opening. 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 (yc.g4fg)on 7p py ux9terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horizontal cord of length L whose other end is fixed k4 ye) gc,g;(n+fd )gxr16v wvqnd5da(Fig. d, gr4dvdeag +)c g1qnwx)kn65y;v f (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 of a 3700-m-high mountain. The climb is madeocv 7 ewm/f7rv4n 6is* in 5.0 h starting at an elevation of 23re 6/vs7 mcv*w4iof7n00 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m auu 1le l1gmn frj*soe8, mx,0au;g75tbove 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;32 e)gjx* nnn xedeb( 47,000 people per hour. If the average lift carries people about 200 m (vertically) high gd2) n3enex xbe;(nj*er, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and np13gy6famt gsh+n8 8osy d8/falls vertically 81 m before striking the turbin1m y+6ogd8nfg 83syspn/t8a he 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 circular vertical loop (Fig.*4- (/eoykq:a;11 q mbz r;wrfe vxtnt 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Show also that as long as your speed is above the minimum neededr e oynea(k 1r bvm4:/q*1fw;tqzt -x;, 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 dire jj06 6uvkyir8ctly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000kJ)y0 k8juiv6r j6    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 atbg(a)u ,kr*mz an upward angle of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, ta7v2f+ciq x jlbfuy/ml*( -e6he spring inside the scale compresses 0.60 mm, and it tells you your weight is 710 N. Now if you jiav7 yl cffqx*/2u(-+6 elmbjump 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, and swings ouqbj+ qlj5hyo-/k9eabn3i )z8 t over a lake (Fig. 6–45). He releases the rope when his velocikyoibnj+z l-9)b/5hae q83qj ty 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 rd 5dmeltx05s5k(dd+ 9.0 s. What minimum power e5srdmx(5dl d+d t0 5koutput was used to accomplish this feat?    W

  Some electric-power companies use water to su7bl1ww mh/eg l 3+p7gyc-u b*tore energy. Water is pumped by reversib7p c*u+e 3-wwu7bly/ l1 ghbmgle 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 stiffness constant k is cut in half. What is the spri6 wff82;sjpi raz;(ihng stiffness constant for each of the two result fjiw;hi6fp8(zsa2; r ing springs?   k

  A 6.0-kg block is pushed 8.0 m u4g3 o0rr/wkjmp a rough 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelerate from 35km/h to 55km/h in 3.2 s, how kks y. zy4o6++bdfn9ylong will it take to accelerate from 55km/h to 75km/h Assume the s46ky ndfz.+oy9 kb+ypower stays the same, and neglect frictional losses.    s

  In a common test for cardia (e- i)if0is,nuq kx5*ow5egac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power required from a 75-kg patient when the trnue5f5qx, ) iiio-se0*akg w (eadmill 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 d2wx)ev7o 4tbgjuup rz60 . i0eistance of 500 m, what was its velocity whe7z60xtvu )oegir e0p.uw b2j4n 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 from a height of 2.0 m a0wtlb z:6(my2ccayy-c hnv6pn :i; 3l t a rate of 95kg/s (a) If this water wheel is set up to:0l y;acly6mwcti2ycp:bvn3z - h 6(n 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