Problems
105
Figure P4.35 represents the total acceleration of a parti-
cle moving clockwise in a circle of radius 2.50 m at a
certain instant of time. At this instant, find (a) the radial
acceleration, (b) the speed of the particle, and (c) its tan-
gential acceleration.
35.
36.
A ball swings in a vertical circle at the end of a rope 1.50 m
long. When the ball is 36.9° past the lowest point on its
way up, its total acceleration is (#22.5ˆi& 20.2ˆj) m/s
2
. At
that instant, (a) sketch a vector diagram showing the com-
ponents of its acceleration, (b) determine the magnitude
of its radial acceleration, and (c) determine the speed and
velocity of the ball.
37.
A race car starts from rest on a circular track. The car in-
creases its speed at a constant rate a
t
as it goes once
around the track. Find the angle that the total acceleration
of the car makes—with the radius connecting the center of
the track and the car—at the moment the car completes
the circle.
Section 4.6 Relative Velocity and Relative
Acceleration
38.
Heather in her Corvette accelerates at the rate of
(3.00iˆ # 2.00jˆ) m/s
2
, while Jill in her Jaguar accelerates
at (1.00iˆ & 3.00jˆ) m/s
2
. They both start from rest at the
origin of an xy coordinate system. After 5.00 s, (a) what is
Heather’s speed with respect to Jill, (b) how far apart are
they, and (c) what is Heather’s acceleration relative to
Jill?
39. A car travels due east with a speed of 50.0 km/h. Rain-
drops are falling at a constant speed vertically with respect
to the Earth. The traces of the rain on the side windows of
the car make an angle of 60.0° with the vertical. Find the
velocity of the rain with respect to (a) the car and (b) the
Earth.
40. How long does it take an automobile traveling in the left
lane at 60.0 km/h to pull alongside a car traveling in the
same direction in the right lane at 40.0 km/h if the cars’
front bumpers are initially 100 m apart?
A river has a steady speed of 0.500 m/s. A student swims
upstream a distance of 1.00 km and swims back to the
starting point. If the student can swim at a speed of
41.
1.20 m/s in still water, how long does the trip take? Com-
pare this with the time the trip would take if the water
were still.
42. The pilot of an airplane notes that the compass indicates a
heading due west. The airplane’s speed relative to the air
is 150 km/h. If there is a wind of 30.0 km/h toward the
north, find the velocity of the airplane relative to the
ground.
43.
Two swimmers, Alan and Beth, start together at the same
point on the bank of a wide stream that flows with a speed
v. Both move at the same speed c(c ( v), relative to the wa-
ter. Alan swims downstream a distance L and then up-
stream the same distance. Beth swims so that her motion
relative to the Earth is perpendicular to the banks of the
stream. She swims the distance L and then back the same
distance, so that both swimmers return to the starting
point. Which swimmer returns first? (Note: First guess the
answer.)
44. A bolt drops from the ceiling of a train car that is acceler-
ating northward at a rate of 2.50 m/s
2
. What is the acceler-
ation of the bolt relative to (a) the train car? (b) the
Earth?
A science student is riding on a flatcar of a train traveling
along a straight horizontal track at a constant speed of
10.0 m/s. The student throws a ball into the air along a
path that he judges to make an initial angle of 60.0° with
the horizontal and to be in line with the track. The stu-
dent’s professor, who is standing on the ground nearby,
observes the ball to rise vertically. How high does she see
the ball rise?
46.
A Coast Guard cutter detects an unidentified ship at a
distance of 20.0 km in the direction 15.0° east of north.
The ship is traveling at 26.0 km/h on a course at 40.0° east
of north. The Coast Guard wishes to send a speedboat to
intercept the vessel and investigate it. If the speedboat trav-
els 50.0 km/h, in what direction should it head? Express
the direction as a compass bearing with respect to due
north.
Additional Problems
47.
The “Vomit Comet.” In zero-gravity astronaut training and
equipment testing, NASA flies a KC135A aircraft along a
parabolic flight path. As shown in Figure P4.47, the air-
craft climbs from 24 000 ft to 31 000 ft, where it enters the
zero-g parabola with a velocity of 143 m/s nose-high at
45.0
o
and exits with velocity 143 m/s at 45.0° nose-low.
During this portion of the flight the aircraft and objects in-
side its padded cabin are in free fall—they have gone bal-
listic. The aircraft then pulls out of the dive with an up-
ward acceleration of 0.800g, moving in a vertical circle
with radius 4.13 km. (During this portion of the flight, oc-
cupants of the plane perceive an acceleration of 1.8g.)
What are the aircraft (a) speed and (b) altitude at the top
of the maneuver? (c) What is the time spent in zero grav-
ity? (d) What is the speed of the aircraft at the bottom of
the flight path?
45.
30.0
°
2.50 m
a
v
a = 15.0 m/s
2
Figure P4.35