7. PROJECTILE MOTION CHARACTERISTICS
The projectile has:
•a constant horizontal velocity and
•a vertical velocity that changes uniformly under
the influence of gravity.
8. If an object is projected horizontally, its motion can best
be described by considering its horizontal and vertical
motion separately. In the figure we can see that the
vertical velocity and position increase with time as those
of a free-falling body.
Note that the
horizontal distance
increases linearly
with time, indicating
a constant
horizontal velocity.
10. Take this basketball shot as an example. Notice the
horizontal velocity of the ball. Look at the spacing of the
vertical lines which mark the position of the ball every 10th of
a second. The spacing is quite consistent, which indicates a
constant horizontal velocity.
14. 3.6 A ball is thrown horizontally with a velocity of 12 m/s.
How far has the ball fallen 2 s later?
HORIZONTAL VERTICAL
vox = 12 m/s voy = 0 m/s
t=2s g = 9.8 m/s2
t=2s
vox = vx y = ½ gt2
x = vx t = ½ (9.8)(2)2
= 12(2) = 19.6 m
= 24 m
15. 3.7 A rifle with a muzzle velocity of 200 m/s is fired with its barrel
horizontally at a height of 1.5 m above the ground.
a. How long is the bullet in the air?
HORIZONTAL VERTICAL
vox = 200 m/s voy = 0 m/s
y = 1.5 m
1 2
y gt
g = 9.8 m/s2 2
2y 2(1.5)
t = 0.55 s
g 9 .8
16. b. How far away from the rifle does the bullet strike the ground?
x = vx t
= 200(0.55)
= 110 m
17. 3.8 A ball is rolled off the edge of a table 1 m high with a horizontal
velocity of 1.8 m/s. With what velocity does it strike the floor?
HORIZONTAL VERTICAL
vox = 1.8 m/s voy = 0 m/s
y=1m
g = 9.8 m/s2
2 2
We need to find the resultant velocity: v f vx vy
Where: 1 2
vx = vox = 1.8 m/s y gt
2
vy = voy + gt
2y 2(1)
t = 0.45 s
g 9 .8
18. vy = 0 + 9.8(0.45)
= 4.4 m/s
vf (1.8) 2 (4.4) 2 = 4.75 m/s
19. THE MONKEY AND THE ZOOKEEPER
The monkey spends most of its day hanging
from a branch of a tree.
The zookeeper feeds the monkey by
shooting bananas from a banana cannon to
the monkey in the tree.
The monkey usually drops from the tree the
moment that the banana leaves the muzzle
of the cannon.
The zookeeper is faced with the dilemma of
where to aim the banana cannon in order to
feed the monkey. If the monkey lets go of
the tree the moment that the banana is
fired, then where should he aim the banana
cannon?
20. The zookeeper aims above the monkey (perhaps he
presumes that gravity will accelerate the banana downward
such that it hits the monkey). What would be the path of the
banana? Would the banana hit the monkey?
Since both banana and
monkey experience the
same acceleration each
will fall equal amounts
and the banana misses
the monkey, moving over
his head.
22. The zookeeper aims
at the monkey and
shoots the banana.
Since both banana
and monkey
experience the same
acceleration each will
fall equal amounts the The key to the zookeeper's
banana reaches the dilemma is to aim directly at
monkey! the monkey.
SHOOT THE MONKEY