Question

A tennis ball is thrown horizontally at a speed of 10 m/s from the top of a building 78.4 meters high. how long does it take the ball to hit the street?

Answer 1

When it comes to horizontal projectiles, the formula for time is:

$t = \sqrt{ \frac{2dy}{g} }$

Where:
dy = vertical distance or height
g = acceleration due to gravity
t = time

Based on the problem, we know that the height at which the tennis ball was thrown is 78.4 m and the acceleration due to gravity is a constant 9.8m/s2. All you need to do is input that into our equation:
$t = \sqrt{ \frac{2dy}{g} }$
$t = \sqrt{ \frac{(2)(78.4m)}{9.8m/s^{2}} }$
$t = \sqrt{ \frac{156.8m}{9.8m/s^{2}} }$
$t = \sqrt{16s^{2}}$
$t = 4s$

The time it would take is 4 seconds.