Question

A ball thrown horizontally at 12.6 m/s from the roof of a building lands 20.0 m from the base of the building

Answer 1

Answer:

1.59 seconds

12.3 meters

but if you are wise you will read the entire answer.

Explanation:

This is a good question -- if not a bit unusual. You should try and understand the details. It will come in handy.

Time

Given

a = 0 This is the critical point. There is no horizontal acceleration.

d = 20 m

v = 12.6 m/s

Formula

d = vi * t + 1/2at^2

Solution

Since the acceleration is 0, the formula reduces to

d = vi * t

20 = 12.6 * t

t = 20 / 12.6

t = 1.59 seconds.

It takes 1.59 seconds to hit the ground

Height of the building

Givens

t = 1.59 sec

vi = 0     Another critical point. The beginning speed vertically is 0

a = 9.8 m/s^2   The acceleration is vertical.

Formula

d = vi*t + 1/2 a t^2

Solution

d = 1/2 a*t^2

d = 1/2 * 9.8 * 1.59^2

d = 12.3 meters.

The two vi's are not to be confused. The horizontal vi is a number other other 0 (in this case 12.6 m/s horizontally)

The other vi is a vertical speed. It is 0.