In what ways is the word “workyk3 s7-x qqqu6” as used in everyday language the same as that defined in physics? In why7xqqk -3uq6sat ways is it different? Give examples of both.

Can a centripetal force ever do work on 4vs7g(oc-9 +dgb ujth an object? Explain.

Can the normal force on an .o+i a 1mmdn gb/6ubi(object ever do work? Explain.

A woman swimming upstream is not moving with respect to jrh d,i 6seeghg6 7,/gthe shore. Is she doing any work? If she stops swimming and merely floats, is work done on gg /i,egj6hd7,6r ehs her?

Is the work done by kinetic friction forcesdol,q,l/jo4 l8pw ,qu always negative? [Hint: Consider what happens to the dishes when you pull a tablecloth out f lq/oo d8p4jqu ,w,ll,rom under them.]

Why is it tiring to push hard -saa lfnlwt g70tt;/9against a solid wall even though you are doing no wg-wlt9a7lt f/a0s;t nork?

You have two springs that are identical except that spring l i e 1d mobwaj1z)j-t 8;syqmi87cdcqu;:c (9 wrs stiffer than sprec;w-q)t m(o:1 1;csrjz7jqw8yimc dbad98u ing 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 h+gt nbvr a:/t qc)6r-d 4zr6myorizontal force on a block that is free to slide on a frictionless surface (Fig.6-30). The block rgt: /+q m4r)-a6zbtdyv6rnc starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential enkmi 9ns z65d*uergy change when yo9*idn k 6usmz5u jump as high as you can?

In Fig. 6–31, water balloons are tossed from the roork8f3k (a yv9kf of a building, all with the same speed but with3vy8 ka9(kkf r different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a height h above its lowenu/opts 86zdpv45w /,2 emqrmst point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial sp 8vpurmnq/t52 oe4m, d6swzp/eed 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 compres;ii8 5nygg2fch:n0s7zqw n(s s the spring by press sq0s2 iyiz:n;h8fwn5gn g7 c(ing 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 w as73yq-z6cm the 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 instructorwc am37sq 6yz- is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy 7tx9 rqtftiwj0b1a,7rmq cd,(( q p. gwhen water at the top of a waterfall falls to the pool bel,ip7(t bc1qg(m a.dt txrfqq jw 9,07row?

Describe the energy qx29g f4(xx cwtransformations when a child hops around on a pogo stick.

Describe the energy transformdme t;:sls 8vk .2hh;-e1 pz0cykl;aoations that take place when a skier starts skiing down a hill, but after a time is brought dseao p e lctvh l;;8k1hm:s02.;y-zkto rest by striking a snowdrift.

A child on a sled (tot51:5df7atmd3q 5g.u m4m1koptkco cral mass m) starts from rest at the top of a hill of height h and slides down. Does the velocity at the bqt 3tr1mc dod.o5k5 akp5u 4g mf1cm7:ottom 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 3eyi* kwf x1e0 nth47zin their path rather than stepping on yw0i 7kf*ne t4zh3x1e top and jumping down on the other side. Explain.

Two identical arrows, one with twice the speed of t pilo/l/c.uj7a e)r *q2xxqa8he other, are fired into a bale of hay. Assuming the hay exerts a constant frictioxpjro)./ 7aluiqcxq*a/ 28e l nal force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple swinguh 9.g0v6de p9g:hpfiing pendulum in terms of energy, (a) ignoring friction, and (b) taking friction intg:i6 .9phveg0 d ufp9ho account. Explain why a grandfather clock has to be wound up.

When a “superball” is dropped, can it rebound to a heightx 8)2bgb;q/w7xknzu w greater than its original height? Expwq)bb x7wzg;kx/ u8n2 lain.

Suppose you lift a suitcase from the floor to a table.szn in x786nnugo8;mks(a. :q The work you do on the suitcase d6o.mx7qnks( nsui:z8 ;a 8ngnepends 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 power needed xpbxk uymi28++ yg9- srather than the work.

Why is it easier to climb a mountain via a zigzag trail than to cli3 tbd tx1 mgczl2(q+o:mb straight upx(lbzgt+ m2t3 1cd:q o?

Recall from Chapter 4, Example 4–14, that you can usel oaji7r3lbenzd; :95 a pulley and ropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for every meter the lolj:3ie5brzl 7; oda n9ad is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when a 265-kg pile driver fallv3 fk9w6.ceok s 2.8v kwoe f9c6k3.0 m?    J

  A 65.0-kg firefighter climbs a flight of stairs 20px i3k6pao k0hk9*5 fw.0 m high. How much work is requiredi6ph 9k5 k0*pwakf3xo?    J

  A 1300-N crate rests on the floor. How much work is reqn+9nc2yb 8l fmuired to move it at constant speed (a) 4.0 m along t+2 f8 nl9cbmynhe floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers dog x 6.7nahpdz16.n y23t edwdx (horizontally) pushing a 160-kg crate 10.3 m across a rough floor without acceleration,3hxntdzd en ..gp 6x1ya27d6w if the effective coefficient of friction was 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rat.(zoy :*ugnsue of for 7.0 s. Find the net work dozu( .uog n*:ysne on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a table. How 7 ry0,b8gjxwqdgr ;i9much work is required to stack them one on top of anoth 7r0 xqri89gjg;dw,y ber?    J

A lever such as that shown in Fig. 6-35 can be used to liff objects we mig *,hr enp g4w)2bbgyy5ht not otherwise be able to liff. Show that the grn5y,pb2* ebh4g )yw 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° incline and is kept from accelerating b1sk h *wd *w;0b crknbe,oa/n*y a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficinob/hb 0*,ewr;ks ck*1a dw* nent 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 M an acceleration)xf9 noq o/zk57su j0q(ztkp9 of 0.10 g uq 0x/o9 ktq(zo5npzf7 9ku s)jpward.    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 thsqrmv81l 6m0t e;s+aipqu1+s e distance axis is linear and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, variesds gnk 7i+/q3rkl5 bk. as shown in Fig. 6–37. Determine the work done by this force to move the object (a) from .n3+qrdi klg/sk b 7k5x=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 m4k;wua1o0 wm 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,.a:ct)w 6z j;pkq++ ecdm+b9c q) pwme an 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 hanfzndi1.li4 xf 0h7 8ps its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required qx hs)k1wl rb hq3(6jhbx .xfcn+ ,a++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 done to stop a 12lkfx1;+ ,hn )r 7 vo3xved- i)) aqsx)nyszo3w50-kgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whos+a206gjti2n qox 2bvc e string exerts an average force of 110 N on the arrow over a distance of 78 cm. What is the speed of the arc2xo b2qatj0i2+ v6ngrow as it leaves the bow?    m/s

  A baseball (m=140kg) traveling 32m/s moves a fielder’s glove backward 25 cm w7ba) dbhz wbhn7px*c;ky,7 r 7hen the ball is caught. What was the ave7x w7zd7bp c)*;y7bnr,kh ahbrage force exerted by the ball on the glove?    N

If the speed of a car is increased9 sty 0nm/ibyw rnoz23e+6+frch o(j2 by 50%, by what factor will its minimum braking 920+w/(6hen ym +frorjbnotyi z3 2scdistance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, invujh 6,,o0s 5qqiitz-t estigators 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 6t-j ,, htzi5sqiqu 0odata 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 ofq7l9w:km+ bt f 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between wlb:9mqt7k f+ the plate and the pitcher is about 15 m.    N

  How high will a 1.85-kg rock gc yt 4 ztcy)cf9,0hfj;4em(quo if thrown straight up by someone who does 80.0 J of work on it? Neglect air resistte4 qcchufm)(fcy40, z ;j9ytance.    m

  A 285-kg load is lifted 22.0 m vertically with an acceleration by a single cda .z hcvimt,55 wxkhgj4f443i8 h.zgable. Deterfvhiga5khzwj izh.g48x5t3 4mc.d 4 ,mine
(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 constanx: i:6z-6i jsu ppjt8yt, k, of 440N/m How much must this spring be stretched to store 25 J of potential eneuxs-tipj8:6yz6 i jp:rgy?    m

  A 7.0-kg monkey swings from one branch to another 1.2 m higher. What isnjmhfg: h1 -x1 the change in potential energy? h1fjm 1 hn:g-x   J

  By how much does the gravitational potential energy ofgjuc.s4e0 o3 3ji -orx a 64-kg pole vaulter change if his center of mass rises je3su0goix-3c. 4roj about 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surfa0ctsu2w.3121nvpd6 lif f dgkce has speed v = 65 km/h when it strikes a horizontal coiled spring and is brought to rest in a dista cp1ft2gvk23 u1d fsd0li.n6wnce 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-kgqb ce deki5mhclev a1 mkn;8w5m3-8)5 book from the ground so it is 2.20 m above the ground. What is the potential energy of thma853i q;bhm5-8 le ewmnkk5d1ec v )ce 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 ;nx. +a( qulmbleoc39of 1600 m and climbs to the top of a 3300-m(cmlu ;+.n xq3a b9leo peak.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m mg+aqf z)3a1t1 -+wddjx f)nnhangs 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 thejn1)+q 3aatdfg 1d )xfwm- zn+ spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is running at top speeddvsgr 9(m2u xe51yt*+9zsf xyi )zhg; (5.3m/s) and grabs a vine hanging verticall)z stxy51mei2 99vgx ;*dzry +h (usfgy from a 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 frictionlesq+qx)+j f pt)gs 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 frictionlmpervh9 ef:* :ess 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 tra0nu mbz(ye7;v3 uo8j *: hju;biskzd+nsformed into gravitational potential energ* bku voeud;i nbyuz+8;07h(3s: j zmjy without the aid of a pole. With what minimum speed must Fran leave the ground in order to lift her center of mass 2.10 m and 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 w mh89khi hl)q,z8q6b/ -nzsw qith a speed of 5.l-m/ 8h wqqzsbkhn,9ih) 6q 8z0 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 mas +n2 dqrh6y- (:mg fs9pjldem*s), whose spring stiffness constant is 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 qlrp h:fd*y9jmg (6 +med2ns- when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides withou moif5a py+jfn(08 ll.t friction along the looped track shown in Fig. 6–39. If the block is to remain on the track, even a 8+i l(ln.0 jfpfma5yot 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 att+h+3)0mcecuwch)z9y) 6pnk u , tknb iached to the end of a spring (spring stiffness constant k), Fig. 6–40. The block is given an initial disple,h+ )ub m9c3 0)+icu kncp)tkyn6hwzacement $x_0$ 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 bri(rzeyv) wd4 *vdge. She is tied to a bungee cord whose unstretched length is 12 m, and falls a total of 31 m. (a) Ca(rvvz d4w*e)y lculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 * k.u nnwjhnrb//cj *e35,uxk is dragged up to point 1 where it is released from rest. Assuming no friction, calculate the */*k jnb5wr3kxhec,unnu.j / 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 at +z0 p .is6s-.6 vk t z/ikf.da1ujfevyan 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 y:n4/j kruhphn,xr7.x.zywbx1/a8 pthe bottom 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 more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passengersp:p j,/y.847rxnw.nh 1 aukhyxbxz r/.

  A cyclist intends to cycle up)y*q7hf o v1nkv0 /czp 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 o) kx45mzr6 t 5pi17ps6dct )qrpc8uq qf mass 7650 kg and traveling 95km/h in opposite directions, collide head-on and come to rest. dtu5pi8q trx65m 67z )c4qk rc)p1pqsHow 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 highs/a-4f d e2r lmsxm0j- and reaches the bottom with a speed of 2.2m/s How much thermal energy due to friction was fm2 s0 4dx-aslej-r/m generated in this process?    J

  A ski starts from rest and slides down a 22/) lbhdoityv n57:6e l5gz*i z $^{\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 1e;4r*unhwz35c7 bdgvh e 3(ot3.0 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, and it bounces back to a height nrg(o;unm; h4.hj3w xof 1.5 m no4w un x3.j;gh(mh;r.
(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 pulledsb87qj oenvf7:eo9+i (nn 2pk across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of frictio+bkv:n78 7( qpio29onefjesnn is 0.30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fig. 6–41 passes point 1 with m-r b1 60bamyprjz49d a speed of If the average force of friction is equal to ond4ary0m pm6 b-j 1rz9be-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches ee eftd;d7m/ 1b 1nzqil(-14vx;ioagthe foot of a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light haxymds z nr686 7.g*bhorizontal 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 stopph a6z86gxdsry. 7* mbning and turning back. What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is 0l;rc-v sh+9wwrm e5ffirmly attached to a very 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 poslw 0srmw5 r+c-;f hv9eition will it stretch on its first swing?    m

  Early test flights for the space shuttle usedf7 bdl jr42h)5llfu s++ anoa5 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/h (a) af b+)jl+oau5 24sn7 hf5lrd lWhat 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-We fj i;s+xovowi,2/. b motor to lift a 315-kg piano to a sixth-story window 16.0 /x f+vij .s,oe; wobi2m above?    s

  If a car generates 18 hp when traveling7qbo j.lve:eq(l9a,y*gcgke li 8+y / at a steady 88km/h what must be the aver 9qvee 8gg l ejk*/:(yq,l o.by7liac+age force exerted on the car due to friction and air resistance?    N

  A 1400-kg sports car accelerates from rest to 95km/h in 7.4dn0m:gm: ygg; s. What is the average poweg;:: dgn ym0gmr delivered by the engine?$\approx$    hp

  (a) Show that one Britis2p5t7oq ca.k 3s+,0ghbr pzqmh 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 ofufj2l,:a.wxwq p tlr8c(qd91ten expressed in the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h in about 6.0 sf( ,t 0ovn1kq4kazrar2bg38y on the3rka(0vyt8a24k zn b1 r,ofg q level when it is in neutral. Approximately what power (watts and hp) is needed to keep the car traveling at a constant 75km/h.    hp

  How much work can a 3.0-h+mb*bj7 vb:r hp motor 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 v7(f. jhcmci 5 zr91snIf this motion takes 1.5 s, what average pcihrc jn7 s(m.51f9vzower was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a hei grcuv*q2ly */z+av3 ight of 3.60 m. What output rating q2z u*3cval+yi g/v*r(watts) should the pump motor have?    W

  During a workout, the football players at S/khv0md 5l 2 c(7 0yz9qtmbvfmtate U. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined atvd(f hm qvmm/c 20y7 0zkb95lt 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 /h uhvn1sxia)93wpe;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 hill can it 78bo wjt/ae.6jf i2*6ialw gbclimb at a constant speed of 7teb/wwo6ja7fba8 2 j*i.6ilg 5km/h if the frictional forces add up to 650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg 3z6ij,/i2mq +mtpxzd box along a level floor at a speed of 1.2m/s if the coefficient of friction is 0.45xm6 2ipmqdjtziz 3/,+ ?    hp

  A bicyclist coasts down :4njwnx w y) ,f3kue82dd uvl)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 bw/pw(2cj k b;euilt “5mi/h(8km/h) bumpers” that are designed to compress and rebound elastically without any physical damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effectivek /;e( jpcw2bw 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.wsq0 ay5)jo+ga boi;1 0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one)yjoi0aq5 +a;1 sowb g. 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 tgnfw;wz/c2f6vf, 17 hu3-vnuw obs y+he 1936 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 traww3nu7f -,;z2b+yc/vf1hnf vsuog6w veling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding wit,2ioxe .1 f 1yy8qwpbthout friction along the looped track shown in Fig. 6–39 is to remain on the track at all times, even at the very to1p wi1x ytfb,e2y 8q.op 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 a u:4ocw mcsmlce+l owgt6z)il) /5*w3ircraft 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 termin w* ow: /u)etlilw c)z+s3o5lc6mc gm4al 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 9mse.i v2jyh,(Fig. 6h.v29s ,mejiy–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 oe g4iaj7 ei x k0mmc,j(597rvpf a 3700-m-high mountain. The climb is made in 5.0 h starting at a7i 490 e ,5kivgjpcm(exjm7ran 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 eleva(g wj n+l9fwx7tor 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 peopl0sp+ k-pl pgmw 8t*;uve per hour. If the average lift carries people about 200 m (vertically) higher, estimate the power neep;m tw v0spupk8 g-*l+ded.$a\times10^b$ W a =    b =   

  Water flows over a dam aeyeki:p,) h9xpedrh)opv (*r*arp )2t the rate of 650kg/s and falls vertically 81 m before striking the turbine bla2ee,)p rppph*vr) ( ide)9oykaxrh*:des. 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. 6zublxiv,c )e( )l 0+rl–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 needed, this answer doesn’t depend on the size of the loop or how fast you go through it l)(+xb,0uirzvcll)e .    mg

  (a) If the human body could conver(m vod0oub,m o8;l /z,mhd .xit a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=1000ko ,8 b.z,mi (h0mmv/oodlxd;uJ)    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 angv h9/i2dkk*d zle 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 batt x(;vu+( e z,e6 uzy)s7t7oanyz)lohhroom scale, the spring inside the scale compresses 0.60 mm, and it te uso zt(y+h)vu7ne;la6e(, 7zx ) tzyolls you your weight is 710 N. 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 over /ba aee./80 , mhsdsema lake (Fig. 6–45). He r/h0b,a meseas8/ dem.eleases the rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of sahs45p i ev6zj*z,dj ;0tsr15.0 m in 9.0 s. What minimum power output was used to accomplish ,tjsav*4j61;sr e0 pz5zhisdthis feat?    W

  Some electric-power companies use water to store energy. Water is pumped by rev8ka i;-y3 pgyqn:1ej 0lsav.q ersible turbine pum;p0qy 8. lkva3- 1ynejiq:asgps 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 stiffnei(r mtbzh1 )9z+ pdvk)ss constant k is cut in half. What is the spring stiffness constant for each of the two resulting sprini(hr1md b )z+kpzt9)vgs?   k

  A 6.0-kg block is pushed 8.0 m up a rough/m tc1.dgec 0z 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 acc(/baqimy ,ds -elerate from 35km/h to 55km/h in 3.2 s, how long will it take-i amdq/bys,( to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for /d9co7)mdfy epa4n h44*cs oxcardiac function (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estimate the power requimf )4xa* d/47c9 yoo4hndecpsred 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 rm2 k,:/z dvlw7vv7r 5xlhyq 1dock vertically upward a distance of 500 m, what was its velocity when it lefl2 7kdv/yz7hvwqdxvm r 1,l:5 t 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 q6 -u)o0h4msksuw 1e8uk8 u5w7clxlg.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, what is w 4xhu 75cllsguum 0ew1q6- kk)us88oits maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s