Question

A ball is thrown straight up from the ground with an unknown velocity. It returns to the ground after 4.0seconds. With what velocity did it leave the ground?

Answer 1

The ball was thrown at approximately
`19.6m/s`.

Step-by-step explanation:

Assuming that there is no air resistance (or drag) in this question, the time to go up is the same to go down. Therefore, we can assume that it takes 2 seconds to go up and then 2 seconds to go down (4 seconds in total).

On Earth's surface, gravity is approximately
`9.8m/s^(2)`. Notice the
`s^(2)` meaning that gravity is given in terms of acceleration. As it's an acceleration, it means that velocity changes at a rate of 9.8 meters per second. As we have 2 seconds of deceleration going up, we have a starting speed of
`2 * 9.8m/s` =
`19.6m/s` .