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ii. The force of gravity on a 2-kg rock is twice as great as that
on a 1-kg rock. Why then doesn’t the heavier rock fall faster?
12. Observe the motion of the moving disks of an air hockey
game. Explain how Newton’s first, second, and third laws
apply. The disks float on a layer of air, ejected through tiny
holes, so friction is reduced to a very small amount.
13. Compare the effort (or force) needed to lift a 10-kg object
when you are on the Moon as compared to lifting it on
Earth. Compare the force needed to throw a 2-kg object
horizontally ith a given speed when on the Moon as com
pared to on Earth.
14. According to Newton’s third law, each team in a tug of war
(Fig. 4—31) pulls with equal force on the other team. What.
then. determines which team will win?
16. If you walk on a log floating on a lake. why does th
move in the opposite direction’?
17. Mary exerts an upward force of 40 N to hold a ha
groceries. Describe the “reaction” force (Newton’s t
law) by stating (a) its magnitude, (h) its direction, (c
what body it is exerted, and (d) by what body it is exert
18. When you stand still on the ground. how large a force d
the ground exert on you? Why doesn’t this force make
rise up into the air?
19. A bear sling, Fig. 4—32. is used in some national parks
1
placing backpackers’ food out of the reach of bears. Ex
why the force needed to pull the backpack up increasL
the backpack gets higher and higher. Is it possible to
the rope hard enough so that it doesn’t sag at all?
H
F
FIGURE 4—31 A tug of war. Describe the forces on
each of the teams and on the rope. Question 14.
15. Whiplash sometimes results from an automobile accident
when the victim’s car is struck violently from the rear.
Explain why the head of the victim seems to he thrown
backward in this situation. Is it really?
FIGURE 4—32
Question 19.
Problems
(I) Show that a -lh cube of butter. or any other “quarter
pounder weighs about I N.
(I) A net force of 255 N accelerates a bike and rider at
2.20 m/s. What is the mass of the hike and rider’?
(1) How much force is required to accelerate a 7.0-g object
at 10.000 “g’s” (say, in a centrifuge)’?
(1) How much tension must a rope withstand if it is used
’?
2
to accelerate a 1250-kg car horizontally at 1.30 m/s
Ignore friction.
(I) What is the weight ot a 5$-kg astronaut (a) on Earth,
).
2
). (c) on Mars (g = 3.7 m/s
2
(h) on the Moon (g = 1.7 m/s
(d) in outer space traveling with constant velocity’?
(II) What average force is required to stop a 1050-kg car in
7.0 s if it is traveling at 90 km/h?
(II) What average force is needed to accelerate a 6.25-gram
pellet from rest to 155 m/s over a distance of 0.700 in along
the barrel of a rifle’?
98
CHAPTER 4
Dynamics: Newton’s Laws of Motion
(II) A 30.0-kg box rests on a table. (a) What is the w
of the box and the normal force acting on it? (h) A 20
box is placed on top of the 30.0-kg box, as sho
Fig. 4—33. Determine the normal force that the table c
on the 30.0-kg box and the normal force that the 30
box exerts on the 20.0-kg box.
20.0 kg
30.0kg
FIGURE 4—33
Problem 8.
-
Superman must stop a 100-km/h train in 150 m to keep
hitting a stalled car on the tracks. If the train’s mass
l0 kg. how much force must he exert? Compare to
cight of the train.
(‘nnsider a box resting on a frictionless surface. A conit force acts on the box for a given amount of time. aced
‘1mg it to some final speed. Then this process is repeated
h another box. which has twice the mass of the first one.
unpare the final speed of the heavier box to that of the
.1 box.
un
of air resistance is equal to one-fourth of their weight’?
(b) After popping open the parachute. the diers descend
leisurely to the ground at constant speed. What now is the
force of air resistance on the sky divers and their para
chute? See Fig. 4—34.
A fisherman yanks a fish out of the water with an
leration of 3.5 m/s using very light fishing line that has
icaking strength of 25 N. The fisherman unfortunately
s the fish as the line snaps. What can you say about the
s of the fish?
A 0.140-kg baseball traveling 41.0 rn/s strikes the
Ther’s mitt, which, in bringing the ball to rest. recoils
kward 12.0 cm. What was the average force applied by
ball on the glove?
Ii
Estimate the average force exerted by a shot-putter on
0-kg shot if the shot is moved through a distance of
in and is released with a speed of 13 rn/s.
Flow much tension must a rope withstand if it is used to
celerate a 1200-kg car vertically upward at 0.80 rn/s’?
A 7.50-kg bucket is lowered by a rope in hich there is
N of tension. What is the acceleration of the bucket’? Is
up or don?
I) An elexator (mass 4125 kg) is to be designed so that
maximum acceleration is 0.0600 g. What are the maxi
urn and minimum forces the motor should exert on the
pporting cable’?
11) A 65-kg petty thief wants to escape from a third-story
il window. Unfortunately, a makeshift rope made of
beets tied together can support a mass of only 57 kg. flow
iight the thief use this “rope” to escape’? Give a quantita—
‘e answer.
1) A person stands on a bathroom scale in a motionless
levator. When the elevator begins to move, the scale
iieflv reads only (1.75 of the person’s regular weight. Calcu
te the acceleration of the elevator, and find the direction
:1 acceleration.
11) The cable supporting a 2100-kg elevator has a maxi
hum strength of 21.750 N. What maximum upward accelera
on can it gi c the ele ator without breaking’?
I) A particular race ear can cover a quarter-mile track
402 rn) in 6.40 seconds, starting from a standstill. Assum
g the acceleration is constant, how many “g’s” does the
Iriver experience’? If the combined mass of the driver and
ace car is 280 kg. what horizontal force must the road
xert on the tires’?
TI) A Saturn V rocket has a mass of 2.75 x lOu kg and
xerts a force of 33
10’ N on the gases it expels. Deternine (a) the initial vertical acceleration of the rocket. (b) its
elocity after 8.0 s, and (c) how long it takes to reach an alti
tude of 9500 m. Ignore the mass of gas expelled (not realis
ic) and assume g remains constant.
(II) (a) What is the acceleration of two falling sky divers
mass 120.0kg including parachute) when the upward force
FIGURE 4—34
Problem 22.
(11) An exceptional standing jump would raise a person
(1.80 m off the ground. To do this, what force must a 61-kg
person
exert against the ground’? Assume the person
crouches a distance of 0.20 m prior to jumping. and thus the
upward force has this distance to act over before he leaves
the ground.
(Ill) A person jumps from the roof of a house 3.5-rn high.
When he strikes the ground below, he bends his knees so
that his torso decelerates over an approximate distance of
0.70 rn. If the mass of his torso (excluding legs) is 33 kg. find
(a) his velocity just before his feet strike the ground. and
(b) the average force exerted on his torso by his legs during
deceleration.
(III) The 100-rn dash can he run by the best sprinters in
10.0 s. A 62-kg sprinter accelerates uniformly for the first
45 m to reach top speed. which he maintains for the remain
ing 55 ni. (a I What is the average horizontal component of
force exerted on his feet by the ground during acceleration’?
(b) What is the speed of the sprinter o er the last 55 m of
the race (i.e., his top speed)’?
(I) A box weighing 85 N rests on a table. A rope tied to the
box runs verticalh upward over a pulley and a weight is
hung from the other end (Fig. 4—35). 1)etermine the force
that the table exerts on the box if the weight hanging on the
other side of the pulley weighs (a) 30 N. (ii) 60 N. and
(c) 90N.
FIGURE 4—35
Problem 26.
Problems
99
on. A sec
(1) A 750-N force acts in a northwesterly directi
on So that
directi
what
in
exerted
he
must
ond 750-N force
ard’?
westw
points
forces
two
the
of
nt
resulta
the
ball plaer
(I) Draw the free-bodx’ diagram for a basket
(b) while
and
jump,
a
on
ground
the
leaving
(a) just before
).
-1—36
(Fig.
air.
in the
constant
(II) A person pushes a 13.0-kg lawn mower at
, which
handle
the
along
d
speed with a force of 7S.0 N directe
Draw
(a)
).
4—38
(Fig.
ntal
horizo
the
is at an angle of 45.0 to
the
on
acting
forces
all
g
showin
diagram
the free-body
on the
mower. Calculate (h) the horizontal retarding force
upward
mower, then (c) the normal force exerted vertically
person
the
force
the
(d)
and
.
ground
on the mower by the
rest to
from
it
ate
acceler
to
mower
lawn
the
must exert on
force).
1.2 m/s in 2.0 seconds (assuming the same retarding
/7
45
FIGURE 4—38
FIGURE 4—36
Problem 28.
(a) at the
(1) Sketch the free-both diagram of a baseball
it has left
after
(b)
again
and
moment it is hit by the hat,
d.
outfiel
the
toward
the hat and is flying
was found
(II) At the instant a race began. a 57-kg sprinter
22 angIe
a
at
block
g
startin
the
to exert a force of 80 N on
ntal
horizo
the
was
What
(a)
.
ground
with respect to the
exerted for
as
force
the
If
(b)
r?
sprinte
the
of
ation
acceler
starting
0.34 s. sith what speed did the sprinter leave the
block?
1 and F shown in Fig. 4—37a and h
(II) The to forces F
frictionless
(looking down) act on a 29.0-kg object on a
net force
the
find
N.
26.0
F
20.2 N and
1
tahletop. If F
n,
situatio
each
for
ation
acceler
its
on the object and
(b).
(a) and
F
90
L
Problem 32.
ns S(
(11) Redo Example 4—13 hut (a) set up the equatio
is in
object
each
of
a
that the direction of the acceleration
we
13.
4-—
le
Examp
(In
object.
that
of
the direction of motion
tht.
Solve
(b)
.>
masses
both
for
upward
e
took a as positis
le 4—13.
equations to obtain the same answers as in Examp
0.52 m/s
(II) A 7500-kg helicopter accelerates upward at
exerteu
force
lift
the
is
What
(a)
car.
g
1200-k
a
lifting
while
cabk
the
in
tension
the
by the air on the rotors? (h) What is
ter?
helicop
the
to
car
the
ts
(ignore its mass) that connec
ss corc
(11) One 3.5-kg paint bucket is hanging by a massle
mass
a
by
g
hangin
also
.
bucket
from another 3.5-kg paint
a
are
s
bucket
the
If
(a)
39.
4
Fig.
in
shown
less cord, as
two bucket
the
If
(b)
cord’?
each
in
tension
the
is
what
rest.
1 s by thc
are pulled upward with an acceleration of 1.60 m
cord.
each
in
tension
upper cord, calculate the
2
F
120
x
1
F
F
(h)
(a)
FIGURE 4—37
100
CHAPTER 4
Problem 31.
Dynamics: Newton’s Laws of Motion
FIGURE 4—39
Problems 35 and 44.
• \ winchw washer pulls herself upward using the
Let—pulley apparatus shown in Fig. 4 40. (a) How hard
.1 she pull down ard to raise herself slowly at constant
d? ( h) 11 she increases this force b\ It) percent. what
icr acceleration be? The mass of the person plus the
set is 5 kg.
(II) Iwo snowcats tow a housing unit to a new location at
McMurdo Base, i\ntarctica, as shown in Fig. 4 43. The sum
of the forces F’ and Fu exerted on the unit by the horiion—
tal cables is parallel to the line L. and F\
4500 N I)etcr—
mine F and the magnitude of F
F
-—
.
0
0
B
F
101)
FIGURE 4—43
I
FIGURE 4—40
Problein 3(.
Arlene is to walk across a “high wire” strung horiron—
between two buildings 100 m apart. Ihe sag in the
e when she is at the inid-poin t should not exceed 10 as
wn in big. 4 11 If her mass isSO.0 kg. what must be the
HOfl in the rope?
\
mew
Problem 39.
(II) 1hc block shown in Fig. 1 44 has mass 01
7.)) kg and
lies on a smooth frictionless plane tilted at an angle
22.( ) to the horironta I. (a ) l)etcrm i ic the acceleration
LI
of the block as it slides down the plane. (0) If the block
starts from rest 1 2.0 m up the plane from its base, w hat will
be the block’s speed when it reaches the bottom of the
in cliii e
,
.
Hi
I,,•i1t)
FIGURE 4—44
FIGURE 4—41
Problem 37.
loms hang glider supports his weight using the six
cs shown in Fig. 1 42. Lach rope is designed to support
eq ua I tract ion of lam’s weight. Ibm’s mass is 70.)) kg.
hat is t lie tension m each I the support ropes?
Block on inclined plane. Problems Itt and —(I
(II) A block is gi en an initial specl of 1.0 m/s up the 22
plane show n in big. 4 14. (a) I low far up the plane will it
go? ( b ) I low much tune elapses before it returns to its start—
mg point? Ignore friction.
(II) A 27—kg chandelier hangs from a ceiling on a vertical
l1)—m—long wire. (a) What horirontal force would be neces
sar\ t ) displace its position 0. 1(1 in to one side? (I*( What
will be t lie tension m the wire?
0. 1 hen a constant force I
(II) A mass iii is at rest at t
acts on it for a time 1,, Suddenly t lie force doubles to 2 F,,
and remains constant until 1
2,,,. l)etcrnnnc the total dis—
ance traveled from I
0 to r
2i,
(II) Ihc cords accelerating the buckets in Problem 35
(Fig. 4——39) are each 1.0 m long and each has a weight at
2.)) N. I)ctermi ne the tension in each cord at its points
of attachment (highest and lowest points).
.
—
FIGURE 4—42
Problem 3.
Problems
101
2 = 6.0 kg in Fig. 4—46. detei
13.0 kg and in
1
(H) (a) If m
1 is
mine the acceleration of each block. (b) If initially ni
does
long
how
table.
of
the
edge
the
rest 1.250m from
take to reach the edge of the table if the system is allowe
1 be
l.() kg. how large must in
to move freely’? (c) If m
g?
11
at
kept
be
the acceleration of the system is to
(H) A train locomotive is pulling two cars of the same mass
behind it. Show that the tension in the coupling between the
locomotive and the first car is twice that between the first car
and the second car, for any nonzero acceleration of the train.
F
(Ill) Determine a formula for the acceleration of the sx
tem shown in Fig. 4—46 (see Problem 47) if the cord has
nonnegligible mass in. Specify in terms of 11 and R. th
lengths of cord from the respective masses to the puke
±
(The total cord length is /
3
rn
tilj
(III) The two masses shown in Fig. 4—47 are each initial
1.80 m above the ground. and the massless frictionless pu
Icy is fixed 4.8 m above the ground. What maximum heigi
does the lighter object reach after the system is released
[Rint: First determine the acceleration of the lighter ma
and then its velocity at the moment the heavier one hits tE
ground. This is its “launch” speed. Assume it doesn’t h
the pulley.]
Problem 46.
FIGURE 4—45
(II) Three blocks Ofl a frictionless horizontal surface are in
contact with each other as shown in Fig. 4—45. A force F is
). (a) Draw a free-body dia
1
applied to block 1 (mass in
(b) the acceleration of the
Determine
block.
each
for
gram
, and m), (c) the net force on
1
1 rn
system (in terms of m
each block, and (d) the force of contact that each block
12.0 kg and
in
2
m
1
exerts on its neighbor. (e) If nz
(dj. Do
and
(c).
to
(b).
answers
numerical
give
N.
96.0
F
your answers make sense intuitively?
.
—
4.8
1
In
in
2.2 kg 3.2 kg
l80m
1112
FIGURE 4—46 Mass in rests on smooth
horizontal surface. tn hangs vertically.
Problems 47. 48,49, and 57.
FIGURE 4—47
) on a smooth hor
1
(II) Figure 4—46 shows a block (mass ni
that passes over a
cord
thin
a
izontal surface. connected by
hangs vertically.
which
(mfl),
block
second
a
pulley to
(a) Draw a free-body diagram for each block, showing the
force of gravit on each, the force (tension) exerted by the
cord, and any normal force. (6) Determine formulas for the
acceleration of the system and for the tension in the cord.
Ignore friction and the masses of the pulley and cord.
Problem 50.
(III) Suppose the cord in Example 4—12 and Fig. 4—23 is
heay rope of mass 1.0 kg. Calculate the acceleration
each box and the tension at each end of the cord, using tL
free-body diagrams shown in Fig. 4—48. Assume the cord
fairly rigid so we can neglect any sagging.
shown in Fig. 4 23a.
FIGURE 4—48 Problem 51. Free-body diagrams for each of the objects of the system
Vertical forces, F, and F(,, are not shown.
—
in,—
12.0kg
(a)
102
CHAPTER 4
2
F.
,
1
F
Cord
4—
-
—
iji=
1.0 kg
(b)
Dynamics: Newton’s Laws of Motion
FTI
FTI
1 =
in
10.0 kg
(c)
F
Suppose the pulley in Fig. 4—49 is suspended by a
C, Determine the tension in this cord after the mass is
ased and before it hits the ground. Ignore the mass of
pulley.
(III) The double Atwood machine shown in Fig. 4-52 has
frictionless, massless pulleys and cords. Determine (a) the
acceleration of masses m
, ni. and m
1
. and (b) the tensions
3
and F
1 in the cords.
C
1.2kg 32kg
FIGURE 4—49
Problem 52.
1) A small block of mass in rests on the sloping side of a
mgular block of mass M which itself rests on a horizontal
‘L’ as shown in Fig. 4—50. Assuming all surfaces are fric
iess. determine the force F that must he applied to M so
-1 in remains in a fixed position relative to .11 (that is. in
-nt move on the incline).
FIGURE 4—52
ill)
Problem 55.
(Ill) A particle of mass in. initially at rest, is accelerated h
a force that increases in time as F = CP. Determine its
velocity i’ and position x as a function of time.
Ill
M
FIGURE 4—50
Problem 53.
1) Determine a formula for the magnitude of the force F
rted on the large block (m) in Fig. 4 51 so that the
is m
1 does not move relative to in,. Ignore all friction.
.
3
sume m
1 does not make contact with in
i1l
F
i11
(111) A heas steel cable of length L and mass M passes
over a small rnassless. frictionless pulle. (a) If a length v
hangs on one side of the pulley (so L
v hangs on the
other side). calculate the acceleration of the cable as a func
tion of v. (b) Assuming the cable starts from rest with length
V on one side of pulley, determine the velocity i at the
moment the whole cable has fallen from the pulley: (c) eval
uate i for :
L. [Hint: Use the chain rule. d ,‘/dt
(dr/dy) ( dv/ di). and integrate.]
—
3
in
FIGURE 4—51
(III) Determine a formula for the speed i’ of the masses
shown in Fig. 4—46 (see Problem 49) assuming the cord has
mass mc and is uniform. At t = 0, i’ = 0, and mass m is at
1 is a distance 1 from the pulley.
the pulley whereas mass in
Assume the pulley is very small (ignore its dianieter) and
ignore friction. [Hint: Use the chain rule. dc/cit
(dr/dv)(dv/dt). and integrate.]
Iil,
Problem 54.
General Problems
ccording to a simplified model of a mammalian heart, at
h pulse. approximately 20 g of blood is accelerated from
5 rn/s to 0.35 m/s during a period of 0.10 s. What is the
agnitude of the force exerted by the heart muscle?
person has a reasonable chance of surviving an automo
Ic crash if the deceleration is no more than 30 “g’s.” Cal-
culate the force on a 70-kg person accelerating at this rate.
What distance is traveled if brought to rest at this rate
from () km /h?
A 2.0-kg purse is dropped 55 rn from the top of the Leaning
Tower of Pisa and reaches the ground with a speed of
29 rn/s. What was the average force of air resistance?
General Problems
103
A fisherman in a boat is using a “10-lb test” fishing line. This
means that the line can exert a force of 45 N without break
4.45 N). (a) How heavy a fish can the fisherman
ing (1 lb
land if he pulls the fish up vertically at constant speed?
. what max
2
(b) If he accelerates the fish upwards at 2.0 rn/s
imum weight fish can he land?
An elevator in a tall building is allowed to reach a maxi
mum speed of 3.5 rn/s going down. What must the tension
he in the cable to stop this elevator over a distance of 3.0 m
if the elevator has a mass of 1300 kg including occupants’?
A crane’s trolley at point P in Fig. 4—53 moves to the right
with constant acceleration, and the $00-kg load hangs at a
5.0 angle to the vertical as shown. What is the acceleration
of the trolley and load?
2 slide on the smooth (frietionless)
1 and in
The masses in
inclines shown in Fig. 4—55. (a) Determine a formula for the
0 02. and g.
acceleration of the system in terms of ni
1 = 5.0 kg. what value of tn
20 and ni
(b) If 0 = 30 0
would keep the system at rest? What would he the tension
in the cord in this case?
.
Problem 64.
150 g) slides freely down a ramp
A set bar of soap (in
3.0 m long inclined at 9.5 I low long does it take to reach
the bottom? How would this change if the soap’s mass
were 300 grams?
) lying on a frictionless inclined plane is
1
A block (mass in
connected to a mass in, by a massless cord passing over a
pulley, as shosn in Fig. 4 54. (a) Determine a formula for
1 in2, 0. and g.
the acceleration of the system in terms of in
(b) What conditions apply to masses in and 1112 for the
1 down the plane).
acceleration to be in one direction (say. nz
or in the opposite direction?
.
.
Problem 68.
FIGURE 4—55
(including the bicycle) can coast
speed of 6.() km/h because of air
must he applied to climb the hill
same air resistance)?
A 75.0-kg person stands on a scale in an elevator. What does
the scale read (in N and in kg) when (a) the elexator is at
rest. (b) the elevator is climbing at a constant speed of
3.0 m/s. (c) the elevator is falling at 3.0 m/s. (d) the elevator
. (e) the elevator is accel
2
is accelerating upward at 3.0 rn/s
?
2
erating downward at 3.t) m/s
A city planner is working on the redesign of a hilly portion
of a city. An important consideration is how steep the roads
can he SO that even lou-powered cars can get up the hills
ithout sIo ing down. It is gi en that a particular small car.
with a mass of 1100 kg. can accelerate on a level road from
rest to 21 ms (75 km/h) in 13.0 s. using these data. calcu
late the maximum steepness of a hill.
A bicyclist can coast down a 5.0 hill at a constant speed of
6.0 km/h. If the force of air resistance is proportional to the
ci’. calculate (a) the value of the con
speed i’ so that F,jr
stant c. and (h) the average force that must he applied in
order to descend the hill at 20(1 km Ii. The mass ot the
cyclist plus bicycle is $0.0 kg.
Francesca. who likes physics experiments, dangles her watch
from a thin piece of string while the jetliner she is in takes
off from Dulles Airport (Fig. 4—56). She notices that the
string makes an angle of 25 with respect to the vertical
while the aircraft accelerates for takeoff. which takes about
1$ seconds. Estimate the takeoff speed of the aircraft.
in 1
in,
I 25
FIGURE 4—54
Problems 66 and 67.
2 = 1.00 kg
in
1
(a) In Fig. 4—54, if in
will be the acceleration of the system?
and 0 = 30 and the system remains at
mass 1112 he? (c) Calculate the tension
and (b).
.
104
CHAPTER 4
.
in,
in’
If a bicyclist of mass 65 kg
down a 6.0 hill at a steady
resistance. how much force
at the same speed (and the
FIGURE 4—53
1112.
.
.
1
F
and 0 = 30 what
1.00 kg
1
(b) If in
rest. v hat must the
in the cord for (a)
,
a
—
Dynamics: Newton’s Laws of Motion
mg
FIGURE 4—56
Problem 73.
die design of a supermarket. there are to he several
t connecting different parts of the store. Customers
have to push grocery carts up the ramps and it is obvi—
Is desirable that this not be too difficult. The engineer
done a survey and I ound that almost no one complains
ic force required is no more than 20 N. Ignoring triction.
hat maximum aneje (1 should the ramps be built. assum—
full 20—kg grocery cart’?
What minimum force F is needed to lift the piano
11) using the pulley apparatus shown in Fig. 1-57’?
I)eterniine the tension in each section of rope: J:
and .
14
F
iss
-
FIGURE 4—58
Problem 77.
the net horitontal once F that the straps of the restraint
chair must exert on the child m order to keep her fixed to
the chair. ‘heat the child as a piirticle and state any addi
tional assumptions made during your analysis.
A helicopter is to lilt a (1)0—kg magnesium frame at a con
struction site, as shown in Fig. I 59. As the helicopter accel
erates upward at (1. I Sg. ss hat is the magn it tide ot t he tension
I m the cord?
ri
I
a
FIGURE 4—57
FT
Problem 75.
Jet aircralt is climbing at an angle of 45 abos e the horn—
ntal and is also accelerating at 1.5 ni s. What is the total
ce that the cockpit seat exerts on the 75-kg pilot’?
the design process I or a clii Id rest ra I it chair, an engineer
.nsiders the tottowing set ol conditions: A 12—kg child is
mg in the chair, s hich is securely tastcned to the scat ot
automobile ( Fig. 4 5X ). Assume the automobile is
olved in a head—on collision ss I th :inot her chicle. Ihe
tial speed i’, ot the car is 5)) km Ii ii id this speed is
duced to ícru during the cot I iit in tune ot )).2() s. Assume a
ustant car deceleration during the collision and estimate
FIGURE 4—59
Problem 7
ness high—speed 12—car Italian train has ii mass ot o(iu
metric tons (e(i1)U() kg). It can exert :i maximum torce of
4)))) k N horitonta I F against the tracks, v here:is at maxini urn
\elocitv (3(1(1 km Ii). it exerts a force of about IS)) k(’al—
cul;ite ( a 1 its mixi ni u ni acceleration, and li I estimate the
k )rce ot air resista nec at lop sliced
General Problems
105