The question “How far does it travel horizontally ...?” immediately tells us that we
should use the first of the horizontal-motion equations listed on the previous page.
∆x = v 0 xt = (15 m/s)(2 s) = 30 mThe information that the initial vertical position is 100 m above the ground is
irrelevant (except for the fact that it’s high enough that the ball won’t strike the
ground before the 2 seconds have elapsed).
- A projectile is traveling in a parabolic path for a total of 6
seconds. How does its horizontal velocity 1 s after launch compare
to its horizontal velocity 4 s after launch?
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The only acceleration experienced by the projectile is due to gravity, which is
purely vertical, so there’s no horizontal acceleration. If there’s no horizontal
acceleration, then the horizontal velocity cannot change during flight, and the
projectile’s horizontal velocity 1 s after it’s launched is the same as its horizontal
velocity 3 s later.
No Horizontal Change
Once a projectile is
launched, its horizontal
velocity remains constant
during the entire flight.- An object is projected upward with a 30° launch angle and an
initial speed of 60 m/s. How many seconds will it be in the air?
How far will it travel horizontally?
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The total time the object spends in the air is equal to twice the time required to