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PROJECTILE MOTION HW1 - REG
101. Right left: Use the scale 1 cm:
5 m and draw the positions of the
dropped ball at 1-second intervals.
Neglect air drag and assume g= 10
m/s2. Estimate the number of
seconds the ball is in the
air.____________ seconds.
102. Right right: The four positions
of the thrown ball with no gravity
are at 1-second intervals. At 1 cm:
5 m, carefully draw the positions of
the ball with gravity. Neglect air
drag and assume g = 10 m/s2.
Connect your positions with a
smooth curve to show the path of
the ball. How is the motion in the
vertical direction affected by
motion in the horizontal direction?
103. Draw bold vectors to represent the velocity of the ball in the
positions shown below. With lighter vectors, show the horizontal and
vertical components of velocity for each position. With different color
draw acceleration vector in each position.
(a) Which velocity component in the previous question remains
constant ? Why?
(b) Which velocity component changes along the path? Why?
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104. A ball tossed upward has initial velocity components 30 m/s
vertical, and 5 m/s horizontal.
The position of the ball is shown at 1-second intervals.
Air resistance is negligible, and g= 10 mIs2. Fill in the boxes,
writing in the values of velocity components ascending,
and your calculated resultant velocities descending.
1.
Which of the following exhibits parabolic motion?
a. a person diving into a pool from a diving board
b. a space shuttle orbiting Earth
c. a leaf falling from a tree
d. a train moving along a flat track
2.
A bomber flying in level flight must release its bomb before it is over the target. Neglecting air resistance, which one of the
following is NOT true?
a. The bomber will be over the target when the bomb strikes
b. The acceleration of the bomb is constant
c. The horizontal velocity of the plane equals the vertical velocity of the bomb when it hits the target
d. The bomb travels in a curved path
e. The time of flight of the bomb is independent of the horizontal speed of the plane
3.
A piece of chalk is dropped by a teacher walking at a speed of 1.5 m/s. From the teacher’s perspective, the chalk appears to fall
a. straight down.
c. straight down and forward.
d. straight backward.
b. straight down and backward.
4.
At the instant a ball is thrown horizontally with a large force, an identical ball is dropped from the same height Which ball hits the
ground first?
a. The horizontally thrown ball
b. The dropped ball
c. Neither -- they both hit the ground at the same time.
5.
At what part of a path does a projectile have minimum speed?
a. When it is thrown
b. Halfway to the top
c. At the top of its path
d. When it returns to the ground
e. There's not enough information to say.
6.
A dart is thrown horizontally toward X at 20 m/s as shown. It hits Y 0.1 s later. The distance XY is:
3
7.
A boy on the edge of a vertical cliff 20 m high throws a stone horizontally outwards with a speed of 20 m/s. It strikes the ground at
what horizontal distance from the foot of the cliff? Use g = 10 m/s2
8.
A track star in the long jump goes into the jump at 12 m/s and launches herself at 20.0° above the horizontal. How long is she in the
air before returning to Earth? (g = 9.81 m/s2)
9.
A model rocket flies horizontally off the edge of the cliff at a velocity of 50.0 m/s. If the canyon below is 100.0 m deep, how far from
the edge of the cliff does the model rocket land?
10.
Briefly explain why a basketball being thrown toward the hoop is considered projectile motion.
11. Suppose that you are an accident investigator and you are asked whether or not the car was speeding before it crashed through the
rail of the bridge and into the mud bank as shown. The speed limit on the bridge is 55 mi/h = 24 m/s. What is your conclusion?
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ANSWERS:
101. & 102.
Vertical motion is affected only by gravity:
horizontal motion does not affect vertical
motion.
103.
104.
(a) The horizontal component of
velocity remains constant because
no horizontal force acted.
(b) The vertical component of
velocity changes because of
acceleration due to gravity.
1. A
2. C
3. C
4. C
5. C
6. 0.05 m
7. 40 m
10. Objects sent into the air and subject to gravity exhibit projectile motion.
8. 0.83 s
9. 225 m
11. The car was traveling after it crashed through the rail (it covered 24 m in a time of 1 s, the time to fall vertically 4.9 m).
Therefore it must have been traveling faster than 24 m/s before hitting the rail, for some speed was lost in crashing through the rail.
Therefore the driver was speeding.