# A ball's thrown upwards from the roof of a building with a speed of 15 m/s. Velocity of the ball when it's 5 m above the roof?

##### 1 Answer

Feb 20, 2017

#### Explanation:

We can use:

This becomes:

Applying the quadratic formula:

This gives 2 values for

and

These 2 times refer to the object moving up and then returning back down.

Using the convention "up is +ve" we can use:

This becomes:

Using

This is the velocity on the way up.

Using

This is the velocity on the way down.

What goes up, must come down.