In what ways is the word “work” as used in everyday language the same as tiyrrc kk;e*5d)t:p,fhat defik p;) ryitrfk :,c*d5ened in physics? In what ways is it different? Give examples of both.

Can a centripetal force ever do work on an ob2o9k4qpe5.u him +mebject? Explain.

Can the normal force on an oa ;ib86t- inn v(ac2;0ey xu9 pzhdq)vbject ever do work? Explain.

A woman swimming ups yiy15upd exz/s :6-jrkpl*v 5tream is not moving with respect to the shore. Is she doing any work? If she stops swimming and merely floats, is work zjkp/y5-vxru *1 d6s y:lpei5done on her?

Is the work done by kinetic friction forces always d p4)bgmm wxto4**y 5onegative? [Hint: Consider what happens to the dishespom*do 5)4gmt 4wbx* y when you pull a tablecloth out from under them.]

Why is it tiring to push h;txg*g5b4;bo *ax orabd.m8rard against a solid wall even though you are doing no wor ;b4dgr8b.xoxrob5* a* m g;tak?

You have two springs that are identical except that.d 9sska(i;vh 8 jsrv; spring l is stiffer than spridsivasjkr;.( vhs9 ;8 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 horizontal force on l jjh)t8m-zl1;e(l . 2tioqi wa block that is free to slide on a frictionless surface (Fig.6-30). ( t1l-mi.ljo h 8zeqi)lw;t 2jThe block starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitakj .o n2sipf*u*ot/ 7dc+oji0 tional potential energy change when you jump as high as you tcf*d*.j/n i7oo p jku0is2+o can?

In Fig. 6–31, water balloons are tossed from the roof of a b;40alrhn1 *ht14ihkeyz cb0a uilding, all with the same speed but with different launch angles. Which ony l a14cethar 1k0bhh0*iz; 4ne has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h abov+5qj2sbtr 9qce 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,j9 srqc25 +tqb 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 ona8zd05 :rv3v.dnzb( iuz )mnw9mw )qw a table. If you compress the spring by zb)m.dmnv 5:) 8 izvz3a(0wrnqw9wd upressing down with your hand 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. 6–34mqtj1 p k8e9u3). The instructor pulls the ball back and stands against the wall with the ball against his nose. To avqj49mk e1upt 8oid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the r,5djkz4f 1ge gravitational potential energy when water at the top of a waterfall falls to the p g1jz drfe4k,5ool below?

Describe the energy transformations wc1ewle q 2s*v2 t*rvh:hen a child hops around on a pogo stick.

Describe the energy transformations that take place when o(*/z ( gepu*oc/8crrv6uymn a skier starts skiing down a hill (yumr * c6u( zcpng8e*/vor/o, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the top of a 4qk 6udz txvb1p026vehill of height h and slides down. Does the velocity at the botteu0q4xk pvvbt 1d26z6om 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 falllpgpg,i77m i( en log in their path rather than stepping on top and jumping down on the other side. Explain7 i,mgp g7ip(l.

Two identical arrows, one with twice the speed of the ot7 v9jtdlcw/ 0pher, 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 than the slowt0v/ clp79wjd er arrow? Explain.

Analyze the motion of a simple swinging pendulum in terms of energy, (a) ignori 50ar nrlvf76pyc+ h7/bne2v: bzg)bqng friction, and (bgbar6vcfr7)n2b: 5 q v b0/len7zph+y) taking friction into account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a height grg+li:z /lm5wp eater than its original height? Explain.i+wpzll/: g5 m

Suppose you lift a suitcase from the floor to a table. The work you do on thew aq+ dj--3vk:k(hko5jdw l 0b suitcase depends on which of the following: (a) whether you lift it straight up or along aw kd-- lakj dh5q3: w(0o+vkjb more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for the power ne;a flo0 mek7:seded rather than the work.

Why is it easier to climb a mountain via a zigzag trail than to climb 5 jyue2q(vid b1 uytwhsq 9*6+straight uu6t*wd2i( ve + q951shy byuqjp?

Recall from Chapter 4, Example 4–14, that you ckc8:(ege 6dftan use a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the load is raised, how much rope must be pull(6et8 efcg d:ked up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pil+ x)n 8crghuo5ijm. -xe driver falls 2.80 g.8-i+xc )x mujr hn5om?    J

  A 65.0-kg firefighter climbs a flight 8hz pfsk0z 8+)zjtg0tof stairs 20.0 m high. How much work is re0s)z+f j08pkhztzg8 tquired?    J

  A 1300-N crate rests on the floor. How much work is required to m)4t v;k/etcua acu.9)kz, tpeove it at constant speed (a) 4.0 m along the floor against a fric ka e .pueztac/;v)k9t t4uc,)tion force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushing a 160-kgq9n4tb09gyt dgbtf d4b++2qu;a;p bw crate 10.3 m across a rough floor without aat+b 94+ugdygb4;;dt9pb0tqf qbn w2cceleration, if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is 3jtld sv 6k:;laccelerated by a force across a floor at a rate of for 7.0 s. Find the net work done on the b;3dl :6tkvsjl ox.   J

  Eight books, each 4.3 cm thick with mass 1.7 3;gq(a hd)sxvkg, lie flat on a table. How much work is required to stack them one on top of anotherqh xas;vd3)g( ?    J

A lever such as that shown in Fig. 6-35 can be used top rsd64t1qaaz*/gf0nd q -m/j liff objects we might not otherwise be able to liff. Show that the ratio of output fon r1gjam/ -fq ad6/z*t4pd0sq rce, $F_{\mathrm{O}}$, 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 0)bhk vgb.g+vaccelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calcugk+gbvvbh.0 ) late:
(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 tyi eyjqv*,hu irm(:,hrlsps * 6f.;/helicopter of mass M an acceleration of 0.10 g upward.uqpi;(h t*hjm.,/ y6rr iys :,elf *sv    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 di/ug.z 4) ltdtm-btd99ytn 9 mjstance 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 a0 h;rzjux7a98 q 5bgmsxis, varies as shown in Fig. 6–37. Determine the work done by this force to move the object (a)s5xmg7z9q;ha8j r b0u from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

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

  The net force exerted on a particle aceuss+.x/+ ijsm) ccj -ts 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 iw) j ;sz5/w0zuwuko* 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/8mr1gho+dt8gz kr 7 a 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 requied1(u* 9 wb8 dl:ovh84fzxje dmg+a0wred to stop 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 d0gzcq b2 ztw/2one 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 whose string exerts a;4 mm;j7ytj znn average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as it leaves thetnm74jjyzm; ; bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove mfqb*o o cd;.e, p0 nj)k*wzk/zp+u/n backward 25 cm when the ball is caught. What was the average force exerted by the ball on the d*pz.u m j)/;,nbk0w*nc /ep o+kofzqglove?    N

If the speed of a car is increased by 50%, by what factr5f-p ng k(r1zor will its minimum braking distancezprf 1k5ng (-r be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark 6ca(xnd 11 mvi:8mdke to be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s massemda kv :(icmn 168xd1 not matter?)    m/s

  A softball having a mass of 0.25 kg is pitcheu 8bookg9d17 kulx;v5d at By the time it reaches the plate, it may have slowexg lo5uo9u7kd8vb; 1 kd by 10%. Neglecting 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 straight up by so8 3xkwf dsbb+,meone who does 80.0 J of wor b, 8+bxkfwsd3k on it? Neglect air resistance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration 4::y 9gl3u xh lnqfq+q by a single cable. Determinx:l :g h3fq4+qunyq9le
(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,wpv2o-b 6w 3majlm.f61(ll8 jdwejo2 k, of 440N/m How much must this spring be stretched to store 25 J of potenmwf(l2 ojj w6l3a m6dep2v-bjl o1.w8tial energy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What is the ghrfq)/;ku yr4 ; i5umchange rm5hrqygu);;kf /4ui in potential energy?    J

  By how much does the gravitational potential energy of a 64-kg lzsrihr ,rbt;k/(8)g pole vaulter change if his center of mass rises about 4.0 m during the j)rh,k zlsrgti br/8 (;ump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h whenmsh 3w9skm c :s.hh5x5 it strikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What m3ss kh:.mhc5 5sxw 9his the spring stiffness constant of the spring?    N/m

  A 1.60-m tall person lifts a 2.10-kg book from the ground q ;) tq7q tq./thg91nx gxe (siq0twk9so it is 2.20 m above the ground. What is the potential energ.sqq0 9tthgegnqk19iw)7 x(t;x /q qt y 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 330czt/98u 7n05ldz6t2bca la mi0-m peak. z z tcduin 2a/987tm0ball56c
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically next to a ruler. The end of the soub/2 ieeh)o0p/h 9b zpring 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, wherei eh/9)ohb2/ puboz0e will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speed (5.3m/s) and grabs :i:t7u+ 5;tj+cmn+chf. j msx5neb yu a vine hanging vertically from nc. cy n5:u ;+j5mux :jtthm+ ei+b7fsa tall tree in the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictrtmmp4 1xv.(zau c t74ionless 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 fri,jk8 fyvp4 it mb.j89hctionless 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 gravitatir*wgd-5 /hg +dfz 6oazonal potential energy without the aid of a pole. With what minimum speed must Fran leave the grouoh5+d6z/ *dgawrf- zg nd in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platform h; t in+t87gr:f1hiye with:y e hni8i;t71hftr +g 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 stdt yzyb 6gj)69iffness constant is 950N/m is attached to a table and is zjy)g66y bdt9 compressed down 0.150 m. (a) What upward speed can it give to a 0.30-kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped trabvt-l t88x)).zx ,)vjnlt5 pzx.h wvhck shown in Fig. 6–39. If the block is to remain on the track, even at the top of the ctlxbt) zw )-5v,)n xvp ht8.hvz.xl8jircle (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 (spring/atob,dxhbedy (h 7rl:vl9* : olgf5, stiffness constant k), Fig. 6vb f(,*r :l,lgboldhxoe9/aht: dy57–40. 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 dptzjfd)aeavf4n ;1)b+z73qe f/ojeo /k.(k a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Calculate the spring stiffness cons4jv def pj dof3)7n.o f/(;ba)tzaeqekz k+ /1tant 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+jb a:5))9njhjmxp qr 1 where it is released from rest. Assumingranx+95) m)pjjqj :b h 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 speeh:.0jxv 6deg 3kr)jgvd 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 the bottof)l )wc*j5aa rm of an elevator 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 f)5 acjw) arl*more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengers.

  A cyclist intends to cyclej9akj eq*6c *a up a 7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling 95km m+ :.kkkqts3uc97ng2 yo.dbl/h in opposite directions, collide head-on gt 9kubqk 2kom..c sdln+7y:3and 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 hi-hhzejv;ao ) 7gh and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction w v hzh7oa-)ej;as generated in this process?    J

  A ski starts from rest nbcq;,w; .h vm-iz9 jcand 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 trsy i-mqv;h*3j de5w3 xee 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 height of 2.0 m, ajy hkr a )gve()afbsfo 4aen/x9 se +06i-ra+4nd it bounces back to a height of 1.5 m(eay0if4+a9 4g -re/ehnb)sofvakj)6xsr a+ .
(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 ab/ zsgwr-:sd8 cross a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0.30. What is the-ws dzb8 :/rgs final speed of the crate?    m/s

  Suppose the roller coaqfet: c .3pl3n 7+ic0f t)qjgmster in Fig. 6–41 passes 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? The distance qf3:lc)+cmpttgq.jf ni 3 07etraveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot ofg4:dk*ma nbt + 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 uqmqa/-8 m sl9 )oxxnh6ih3 v5very 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 coel3vq69xhq/a mh uon xim)- s85fficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light horizontal sm zzm2i 40yw rre;/ t+rdkhq/+pring, Fig. 6–40. The block can slide awim2/z 0kqm+rhte4 r/rz y+d;long 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 for th4-bmq *si g:vse space shuttle used a “glider” (mass of 980 kg including pilot) that was launched horizontally at 500kvq ismb-:4s*g m/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a) What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lift a 315-kg piano tov2qzfw aozuj5 (d6d)uh -)as- a sixth-story window 16.)2-6s-5 qavduua jzwh f)d o(z0 m above?    s

  If a car generates 18 hp when traveling at8b*kl-fp 6h lyo5q6n6gou vfmu(+l t/ a steady 88km/h what must be the average fo6qg865pl-/khl*yl (n+fo b fvo mtu6urce exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerate51/dcu( ooc rbs from rest to 95km/h in 7.4 s. What is the average power delivero r5u cd(b1co/ed by the engine?$\approx$    hp

  (a) Show that one British horsepowhcph(kt8( cat /g0 x8ter$ \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.” uwux+.( c na af3pd62e
(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 (l 3zzycn1lrx7 62zpw slows down from to 65km/h in about 6.0 s on the level when it is in neutral. Approximately what p 3z1yc2ln6rw zzl x(p7ower (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp mo,qejoi 1*om-(bdz1 kstor do in 1.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accelerates a 7.3-kg shot from rest to 14m/s If this motionj0izbw l k:2esw4q2 b8 takes 1.5 s, what average power w8qbi0 wb:s4 kw2 zje2las developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3.65g qzv/xvp6w60 m. What output rating (watts) should the pump 5z /g6vpq6wv xmotor have?    W

  During a workout, the football players at State U. ran up thhyfyqwd zo** /4 /ndk;e stadium stairs in 66 s. The stairs are 140 m long and;ofd n//y** hyk4 wzdq inclined at an angle of 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 68v8 lzx(f0vk i.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 hpv)j90escwjlmz 9/)w e . How steep a hill can it climb at a constant spe eelj )v /wmzws)cj909ed of 75km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor haveo3khlj-rr t8q o(a9 aq*7k;zq to be able to drag a 310-kg box along a level floor at a speed of 1.2m qotk9-zqq orlka8*3a;7(rj h/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down a 7.07xebyz v9/ul1 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpey(vq zrz0a;3d rs” that are designed to compress (0 qz3zr;yv adand 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 remainw 0 fn1f q:ifqc+j.iwhw:)pm:ing four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with whjq p:10wqiff w:cfn:m+.) i 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 longf:mlw2.jp 0 ma jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum spma:.l0 m p2jfweed 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 frihgi9:mchd 9c w0:w 5h au1zf+cction along the looped track shown in Fig. 6–39 is to rem hdhfa+5cwimhc:cuw: 91 zg09ain 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 jumpingi 0 /qn8;fo8:gnrqzyk from an aircraft without his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimzo8i/ rg8nqk;fn:0qy ate
(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 horizontv6:gilv10db;t ev:l7d l niu sh: /bb8al cord of length L whose other end is fixed (Fig. 6–43). bvg 7vdbdlv ::0;e8 6lbi:u/ lt nhis1
(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 the1q*fhbz+7rf u)8 cw gl top of a 3700-m-high mountain. The climb is made in 5.0 h starting at an elevation of 2300 m. Calcu 7grf bqzh8 1luc+f*)wlate
(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 bre2zr 8 tpq-ou5saks when a 920-kg elevator is 28 m above a huge spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its lifts can move 47,000 peox5td:dz k8a w*ui8oy59f3du lhmsw72ple per hour. 2i5f*hk5yd zdlm s8uu8 d xat9oww73:If the average 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 verticamx 7 7nkb yoe;l9rvx(cwgf/k:dk ( xr2p )ds0)lly 81 m before strikinxcx 0b):);pkonr7fdlk2(w x7( dr9g/ykmv esg the turbine blades. Calculate
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circular vertical lfd ;nt b)faz0*oop (Fig. 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 tatd*0f)n ;bzf hat 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 :go:-f taja+r bwe )6xyb0 2bpinto work, how high could+ybwafaoj-rgbx :6:et) bp 02 an 82-kg man 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 an upward angle yo8s*m2 zbj h9of 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside(x- v qra4nkc4 the scale compresses 0.60 mm, and it tells you your weight is 710 N.nqa(4 k r-xcv4 Now if you jump on the scale from a height of 1.0 m, what does the scale read at its peak?    N

  A 65-kg student runs at 5m/s grabs a rope, and swings out wk rti7 pr*ow.-8j gtbaj4*m0over a lake (Fig. 6–45). He releases the rope when his velocity*i48a wkb -7w0.j mrrj tt*gpo 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 9.ps.eg6qmo-v) bt- 8ly0 s. What minimum power output was used to acco) tl-p.8-qvmy ogs e6bmplish this feat?    W

  Some electric-power com/f(i23t3yk hon ga*(oaic:1w xbxw*opanies use water to store energy. Water is pumped by reversible turbine pumps from a low to a high reservoir. To sto ioxt/cb g3w a*x f(*o(wn1:y3ki2oa hre 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 cons k/h qe70ue8vctant k is cut in half. What is the spring stiffness constant for each of the two resu/ ecq v08ue7khlting springs?   k

  A 6.0-kg block is pushedi 9w.at6ozrwtj t4)r2; q a-yu 8.0 m up 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 acce (g59 kgy1pyixlerate 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 ly( gy9 gk5ixp1osses.    s

  In a common test for cardiac function (the “stress test”), the patient q0 (xg med3 ddj8vl(7bzc 0wavxx2x.8j5k . sawalks on andd2wdeq3sj 0 xaxlm8.z7kgx0(vx jbc v (85a . inclined 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,j+ wv6kjw1 bs4 what was its velocity when it left thb6wj 4jvws+1k e 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 at a rate of .j o8,70kgexe mo,dl-pw)cbr3 -zjtl95kg/s (a) If this wat3)dom8-o ew, g-jb0z k,cltjrep.7lx er 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