In what ways is the word “work” as used in everyday language the same as that de +3hjz xr9bvq0fined in physics? In what ways is it different? Give examples q hjrb +0zx3v9of both.

Can a centripetal force s) js+p/.cpkqgkc 67g(daq n9ever do work on an object? Explain.

Can the normal force on an object evetu:f )6 g7huair do work? Explain.

A woman swimming upstream is not p7bqhp; w4vn c1 f q*er/gng07moving with respect to the shore. Is she doing any work? If she stops swimming and merely floa q7 v/b;nqgpnp4ce 7 10rg*hfwts, is work done on her?

Is the work done by kinetic friction forces always negative? [Hint: Consider es.3mv.rgar 5 what happens to3r e.sag.5mv r the dishes when you pull a tablecloth out from under them.]

Why is it tiring to push hard z;0:kj phh6ai against a solid wall even though you are doing no wor:jhphi0 z6; kak?

You have two springs that are identical except that spring l is stiffer than/9 aknvq.xhbj4v a,7b7 hbc m2 spring 2m,xa b972j 7q.hhan4vbcv/k b $(k_1>k_2).$ 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 os *6tlvo y-e:xno7cv3n a block that is free to slide on a frictionless surface (Fig.6-30). The block starts from rest at þoint A, and by the time it*ov:nl-x3tvc6 y7soe 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 enerj-u9*4v) wumwf-aacf+r-xyxirx; j; gy change when you jump as high as yo caya; f xx*)9u-fj; 4 xwr+m-wvrju-iu can?

In Fig. 6–31, water balloons are tossed from the roof of a building, allw)v8gant)qx 5( xip,t(vy )w u with the same speed but with different launch angles. Which one has the highest speed on impact? I(vvitq y8)(,watu) 5x npxg) wgnore air resistance.

A pendulum is launched from a point 1v * h- kp5bt vd8wssxqc868clthat is a height h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is directed upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium po 8d5lxq-*w bvt1p8hkcscs6 v8sition? Explain.

A coil spring of mass m rests upright on a table. If you comg3 y)u3eo1 +,mbf 9h0r zaijajpress the spring by pressing down with your hand and then release it, can the spring3fay ai g1jr,b3h0 oe)mz+ uj9 leave the table? Explain, using the law of conservation of energy.

A bowling ball is hung from the xw ,yibyxk/55 ceiling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avoid injury the inyk 5x i5wb/x,ystructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potenti-bkxl0iw*x xd /zq1 d0al energy when water at the top of a waterfali x* w0ddk1lb/x-0zq xl falls to the pool below?

Describe the energy transformaz v+;c 5b-mu gye4gum8tions when a child hops around on a pogo stick.

Describe the energy transformations that 7hn;cnj */0o r0k rfaptake place when a skier starts skiing down a hill, but after a time is brought to resrp;rfnj */kc a0no7h0t by striking a snowdrift.

A child on a sled (total mad f j fdq1ogn*.nli(0a ..izf7ss m) starts from rest at the top of a hill of height h and slides d.f.a7dljg n* fin1d.q zo(0fiown. 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 step over a fallen log in their path rather tdc):8 og3qd9:l q vuavhan stepping onqv)8l d 3:c: av9odguq top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of mnc.sdau*f) 1the other, are fired into a bale of hay. Assuming the hay exerts a constant frictu ms1)dc*nfa.ional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swingi dpuutl 4odq,59, t5qrng pendulum in terms of energy, (a) ignoring friction, an u4 q,tudtqo p55l9,rdd (b) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can l o1 yhyjw03zjp-6 sql-8,nmbit rebound to a height greater than its original height? Expl-zp ynj6blm8 hw,oql 30j- 1ysain.

Suppose you lift a suitcase from the floor to a table. The work you do on th1vq4 wx(:ongwav7 )pge suitcase depends on which of the following: (a) whether you lift it straight up or along a more complicated paxqv g7 avw1)nog(p w:4th, (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 the workk*i71 t.p;qq 4hygyry2 nhp- f.

Why is it easier to climb a mountain via a zigzag trail than to clevau3q 8lt5s;vd (t9a 3 -afigimb straight u3-qvla u3 i(958fatsea t;d vgp?

Recall from Chapter 4, Example 4–14, that you can use a pulley f,z s0gao(x;r*x 3objx+:k ih and ropes to decrease the force neede3fzh ,oox0xg(x*; br:i+jska d to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitationak35 su -cjefu-l force when a 265-kg pile driver falls 2.80 m?5 -kce-fs 3uju    J

  A 65.0-kg firefighter climbs a flight of stairs 20.0 mq1r7k 9zq:( tdw (;ebo.ydn1jl y 4rhh high. How much work is reqd;dt1lqywnyr9k bh qz7.1( rj4 h(e :ouired?    J

  A 1300-N crate rests on the floor. How much work is reqg *xtj w-8+pjwuired to move it at constant speed (a) 4.0 m along the floor against p jxjwt-*gw+8a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) p.s i0(x .greq;/nvdmf ushing a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient f x 0 ng.rmesq(/di;v.of friction was 0.50?    J

  A box of mass 5.0 kg is acbze sw;:6a(wxcelerated by a force across a floor at a rate of for 7.0 s. Find the net worwzaweb s;( :6xk done on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a iksio1: v:.3dfl+b x wtable. How much work is required to stacxd bs+:o l:kifi1v. 3wk them one on top of another?    J

A lever such as that shown g76xk;w t 7ox6xviyq(in Fig. 6-35 can be used to liff objects we might not otherwise be able to liff. Show that the ratio of ouw7ko 6xx vqytx7ig(;6tput 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° incline and is kept from accelee eg62rjtud6z:*1:zt oc qaq3rating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effectivj ga: r2otz*u:c3tq1z66 qde ee 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 helicopter of mass M1fhnq4m e (fcmajmz+04.t 0z(9ro xcj an acceleration of 0.10 g upward. 9z1fxra z(m 0mc4nhm o j0e.tq+4(cfj   Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is linear amyold swetc7:3): lb 7nd 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 rua:;tnfsrl+r; 3. hdx axis, varies as shown in Fig. 6–37. D d 3u.;:sfnta+;rr hlretermine the work done by this force to move the object (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a nex n9p6s*ar h,l0bs3particle 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 vx+t9x:jg 5 tv(h1x oq zvi2v/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 doubled, by what factor has its speed increased+*azoot u+hq)6 b7acx? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to s 7oithh1i9;uotop 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 18h bpp1 u(eys2250-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average 8ta(c z v)5esfforce of 110 N on the arrow over a distance of 78 cm. What is the sef ct8(av) 5zspeed of the arrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glo ya6ubh 6prx+7ve backward 25 cm when the ball is caught. What was the average force exe67 uxhab+ 6pyrrted by the ball on the glove?    N

If the speed of a car is increased by 50%, by what factor wiw2itj ep2n v +u),9yxh viz0lc3+m7zsll its minimum braking distance be increased, ass)0h 3e2sltm9xyjvz 2p z,cni 7u+ iv+wuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on8jfd5lslw6o8 uv*)txs; kv;o a level road, investigators 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 d);d6 o wj fol5xvs;u *sv8l8ktriver slammed on (and locked) the brakes. (Why does the car’s mass not matter?)    m/s

  A softball having a mass of 0.25 kg is pitched at Be lgjle8:ir ngwd;/ c v (l+wt1-i;g6hy the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average forceng6 e8l-viiwcgw/;(1r+lghld: et ;j 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 s h+7pwrzai. r2traight up by someone who does 80.0 J of work onr7hai2zrp. w+ it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an accd8fhz 21a1/e mpyp6bpeleration by a single cable. De ehpm 1fp/2pzd6 a18bytermine
(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, y b(s9 ;k5ymscu,:y yqof 440N/m How much must this spring b:9q my,(sk5cy y ybs;ue stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one branch 0kl8fuk( oucd + /qmv28 8jjysm,3ldeto another 1.2 m higher. What is the change in potential enejs u8mel 8ck 28vy,d/ + (3kj0lqmuodfrgy?    J

  By how much does the gravitational potential energy of a 64-kg polenoqcu-g-d/:g vaulter change if his centegudcn-q/ :-o gr of mass rises about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surfacep e+x1ydpo5vpaxj0 8; has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought d5ap+x p1j; xe0y8opvto 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/y4tnprq(:qr md4u ) qove the ground. What is the potential energy of the book relative:yrnu4q )pmq4qtd (/r 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 160t5 5n2 czzqg4n)qv0vz 0 m and climbs to the top of a 3300-m pg0v5tz)cqn nzz 5 v4q2eak.
(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 = 53skqidl6v rt033/.k3d2 gkbsjN/m hangs vertically next to a ruler. The end of the spring is next toss6.k3 / kqktbiv03g dj3l2r d 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?    cm

  Jane, looking for Tarzan, is running at top speed (5.k5 2u9*joi- hvc*8uup4bvq bf3m/s) and grabs a vine hanging vertically from a tall tree in the jungle. How high can she swing upward? jo*9h 4p-fivv8 ku*qb5ubc 2u    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest,b *ot ddja78.(jpqv2v*e5tlotwf /8f 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 shove up a frigwf+.c,t (dss ctionless 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 kinethc)l8 09rj cofic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran leave the ground in orderoc fc0hj)8l 9r 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 from h (m+a qs/kx*l)pom:athe top of a platform with a sppxasoh/)(l* k+:ma qm eed 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 consl)cqt ,t qa5c7tant is 950N/m is attached to a table and is compressed down 0.150 m. (a) Wha)7 q ctaqt,l5ct 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 without1 pkmx. 6bfi*q friction along the looped track shown in Fig. 6–39. If the block is to remainf 1q.imkpx*b6 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 to the end of a spring (s kfv3-(gvad82 3p(h u8xj roqlozvz wf)l(e 7-pring stiffness constant k), Fig. 6–40. The block is given an initial displacementajv-u kf z)vg l 3o2(e(z8xv (qfw-h73d8lpor $x_0$ 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 bridgm jn*xrw7(ut 34w8m f 6oktp.ae. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness constant k of tt*wp4a.63x urk j8w f7mnom(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 Figg kv dth5- n/:n5w0lx 1n2 r.i,h+gy3qcrbpyu. 6–41 is dragged up to point 1 where it is released from rest. Assuming no friction, calc5rhuh y: 0nn+k5 ny .gvx2ig1w3b- pl qtc/r,dulate 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 atov),u 3frj)dl( i0i/a :zs gzt 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 elaqlry r xtuq7 rd:-96+evator 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. Let M be the total mass of the elevator and passer t7 r9qq +dl:a-xuyr6ngers.

  A cyclist intends to cycle up a 7.8n+ x crelno:lt*shwz4v-2 43l $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km/h in opposite directic:mske lyw7 p2kmxj5 2n.9 p*eons, collide head-on and come to rest. How m*xkm295n 27 .:jel pcywpmkesuch 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 with a s1q o59+v52eoczw rpn. yter; iaza :d;peed of 2.2m/s How much thermal energy w5; ne 5y;edpzorzv+qca19ar:o2ti. due to friction was generated in this process?    J

  A ski starts from rest andxs df sc43zyqi4g/ s9/8rkp7jp qwr.0 slides down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dropped from a tree 13.0 m above the ground.7y/ajf ccxi6o0g+: ) ms8fmmh
(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 :2qy8h4g uvb* 5pwmw i aq8v5aback to a height of 1.5 m.qa5pbu i q4wag* ym h58vw2:v8
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled across a floor with a constant qzy-co(c* l2m horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the final sc(q*ym2c -ol zpeed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with a t yl3;as3/ypg speed of If the average force of friction is equal to one-fifth of its weight, with what speed will ity ;3 /yagp3slt reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot oug87 /8nagpx/q+4om5igmogdt*- lc df 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 tocg: 66 jn.2h;fpgszxq 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 out 2.3 cm beyond the equilibrium position before stopping and turning back. What is the coefficient of kinetic friction between thez26:g;hsx fpcn .j6gq block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal spring, Fig. 6pbv))es ecm5x cb81y, –40. The block can slide along a table where the coefficient of friction is 0.)xbcb8e)cm p,e5vy1s 30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mas c)so yho93pywlrh 9c0x97fb: s 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/h (a) What would its landing speed have been in the absence of air resista7ohc39:cx yy f9 h oslwr)90pbnce?$\approx$    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 -h 0ku ul ch6xtdc2*6za 1750-W motor to lift a 315-kg piano to a sixth-story window 16.0 m a lkx- 2*ch0hz tu66ucdbove?    s

  If a car generates 18 hp when traveling at a steady 89 kkefsv2, po))3vclg8km/h what must be the average force exerted on the car due to frictfvcsvkl,e)p9ok )2g3 ion and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95yrz :f*/o ;nzmkm/h in 7.4 s. What is the average power deliv/zf: *r;zynom ered by the engine?$\approx$    hp

  (a) Show that one British horsep6ofkao v b,5v *,fs6sr z5+fiuower$ \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,z+gbre 6 x: .akuytl91 0ntfmc8 )orrurs.”
(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 slow)2n.huk47e vrrp racc0d+ p2ws down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to kd .r0aw)k +2 cvp2cr7hp rune4eep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1.0 h? i tbo nk8+)( n7 pmou0w4qvl(u$a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3xqq4l-:c6o/h kl.xfr xuf o .3-kg shot from rest to 14m/s If this motion takes 1.5 s, what . l3/o4x.f :fhcuoqk6xl-xqr average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute throughqpu/wir3-w0w 8tvi0b a height of 3.60 m. What output rating (watts) should thew vbr it00wp38 /w-qiu pump motor have?    W

  During a workout, the football players at d+)koputsd7k. 4v +mumk; pi)State U. ran up the stadium stairs in 66 s. The stairs are 140 k+di;puk 7us )mvd.p4)+ kotmm long and inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclis2yozde6x/i ( wt climb 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 hil-5r;4pbtl bxml can it climb at a constant speed ofx4bblm p;-t5r 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have b( 2nw mi)45muu (p0d. htptisto be able to drag a 310-kg box along a level floor at a speed of 1.2m/s if the coefficient of fs (db(i)5pim 0 ut24t.hu npmwriction is 0.45?    hp

  A bicyclist coasts down7r/q dgn*f +pdmyv)v*db1r v0 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 bui,;an e6mopan0j u or.;lt “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 mupna.ao jn,e;0u6r ;mo st 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 i/uc7c9 va6ud+rcz2 r first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 books, how much work is required to fill all the shelves, assuzdr /i+ 7r 69cvcuc2auming 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 193q g :.d1d3vfnjiyqtqv6n94 0n6 Olympics 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 tr4yn fd 0 :djn9tg.q q316vqnviaveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without fr+yhovnb 3y2lbi(b 4+ yiction along the looped track shown in Fig. 6–39 is to remy(+bn2 h4lb3iv+o y ybain 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 jmtk3mg1vrzpav ;6 3 xf e/go/4umping from an aircraft without his parachute opening. He landed in a snowbankr/41;tkamfz eo 3gm6 xp3 v/vg, 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 r:t0p1e:rx;dbj + zzaxc/q9 s of length L whose other end is fixed (Fig. 6–43):qbas x01/;jzrrt zpxe+c9 :d .
(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 fs7pzn2ol(u0 *jvsw1 7c ccb- mountain. The climb is made in 5.0 h starting at anulcz(s12cs-wpv* cjob nf70 7 elevation of 2300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28qe ,-g,pcgdo. m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,000 peoy m1 62jai;sfaple per hour. If the averajm ai6;21s fyage lift carries people about 200 m (vertically) higher, estimate the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and falls verticmpac gy/j4i; 9e )3zt/ke9rtkaj9 9ufally 81 m before striking the turbine blades.9e4gj9mp eia3f9c/u;y k9z r/ja k)tt 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 (Fed inhwk5s+p28+) rq cig. 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 — tn hdr5q++ki cw) p28eshat 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 cnnhuishc*aqt5e 8 1h57jz 7 )eonvert a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by on1 nst55h )cequ7j ein8zh 7*ahe 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 angle of 4qupu marg*zt)os8 4*65.0$^{\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 0.60 )+/wju;sj lsw(j .h)pwjay-p)dhz q 2 mm, and it tells you your weight is 710 N. Now if you jumjhhs2sjd/w-(yj) j+ zp l );wqw. )paup 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 out 56.s6n6 no fisb0fd1. ixwbbjover a lake (Fig. 6–45). He releases the rope when his v6 1f.w. bbnijo65xdf s nbs06ielocity 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 disbw) gox)i/q1k2+b chj uv-h b1tance of 5.0 m in 9.0 s.hj wuq -x 2+1b/bg 1o))hicbkv What minimum power output was used to accomplish this feat?    W

  Some electric-power companies use water to store energy. Water is pumped by bf v;-wl vp0r wz,/3hhhiww4 2reversible turbih34vrhiwbwflw0 /h v,-2w ;z pne 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 in8d/7xx tb kn2ol( m-xjvqe.c8 half. What is the spring stiffness qt j(kxl8/8xd o2xcbv.m -n7econstant for each of the two resulting springs?   k

  A 6.0-kg block is pushed 8.0 m up afd(wu 9-k vl60ketgt ,*7 e:6rwhdzpn 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 accelerat0k:+ llrfmq 8ce from 35km/h to 55km/h in 3.2 s, how long will it take to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional cqf+m80 : kllrlosses.    s

  In a common test for cardiac function (the “stress test”), the patient walka;dc/*z 0jgy is on an inclined i/da* z0jy cg;treadmill (Fig. 6–46). Estimate the power required 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 500-kg rock vertically upward a distance of 500 m, wha:l9)y phq.go c*qsjuldt5a /;t was its velocity when it left the volc*)9q5d tg.p y;qhc/:lso jalu ano? $\approx$    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 fro+n go -kq;:eezm a height of 2.0 m at a rate of 95kg/s (a) If thiz+q:egk e- ;ons water wheel is set up to provide electricity output, what is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s