Question

A tennis ball is thrown vertically upward with an initial velocity of +8.0 m/s. What will the ball's speed be when it returns to its starting point? How long will the ball take to reach its starting point?

Answer 1

I found `1.6s`

Explanation:

Assuming no air restance the speed when the ball comes back to the starting point will be again `8m/s` but directed DOWNWARDS; we can express this saying that it will equal to `-8m/s` adding a minus to indicate the downward direction.

To find the time of flight we use:
`v_f=v_i+at`
Where:
`a` is the acceleration of gravity (downwards, `-9.8m/(s^2)`);
`v_i=+8m/s`
`v_f=-8m/s`
So, we get:
`-8=8-9.8t`
`-16=-9.8t`
`t=16/9.8~~1.6s`