1
Chap4HW1 Questions
7.
An airplane flying horizontally at a constant speed of 350 km/h over level ground
releases a bundle of food supplies. Ignore the effect of the air on the bundle.
What are the bundle's initial (a) vertical and (b) horizontal components of velocity?
a)
v
oy
= 0 km/h,
b)
v
ox
= 350 km/h,
(c) What is its horizontal component of velocity just before hitting the ground?
There is no significant horizontal acceleration so
v
x
= 350 km/h,
(d) If the airplane's speed were, instead, 450 km/h, would the time of fall be longer, shorter,
or the same?
Same.
Time of fall is determined by vertical acceleration and vertical initial velocity
9.
Three paths are shown for a football kicked from
ground level.
Ignoring the effects of air, rank the paths
according to
(a) time of flight,
Since they all rise to the same height, they all tie;
(b) initial vertical velocity component,
Since they all rise to the same height all tie
(c) initial horizontal velocity component
They have different horizontal initial velocities
because their ranges are different:
3, 2, 1;
(d) initial speed, greatest first:
3, 2, 1
Problems
17.
A projectile is fired horizontally from a gun that is 45.0 m above flat ground, emerging
from the gun with a speed of 250 m/s.
(a) How long does the projectile remain in the air?
Know that
2
0
2
1
at
t
v
y
y
oy
+
+
=
Choose origin at initial position of ball so
y
o
= 0
and
y
= 45 m
Since the ball is fired horizontally
0
=
oy
v
Therefore
()
s
03
.
3
m/s
9.8

m
45
2
2
2
=
−
×
=
=
a
y
t
(b) At what horizontal distance from the firing point does it strike the ground?
Since there is no horizontal acceleration,
t
v
x
x
ox
=
−
0
= 758 m
(c) What is the magnitude of the vertical component of its velocity as it strikes the ground?
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 Spring '08
 oshea

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