Question

PROJECTILE MOTION

A cannon shoots horizontally off a 90 m high cliff with a speed of 90 m/s. How much time until the cannonball hits the ground?

Answer 1

All you're interested in is stuff going on in the vertical direction. This means its horizontal speed doesn't affect your answer. So what do we know?

Starting vertical speed, v0 = 0 m/s (cannonball starts from rest)
Vertical acceleration, a = 9.8 m/s^2 (gravity)
Vertical distance, d = 90 m (height of the cliff)

We want to find time, t. What equation can we use to solve for t using the variables we already have?

Answer 2

\( \color {maroon}{\text {This}~\text {is} ~ \text {what}~ \text {I've}~\text{done}\text{:}}\)\[\Delta_y=V_yt+\frac{1}{2}at^2\]\[-90=-4.9t^2\]\[t=4.29 s\]

@matt101

Answer 3

Looks good!