Question

A tennis ball is thrown vertically upward with an initial velocity of +6.2 m/s. What will the ball’s velocity be when it returns to its starting point? The acceleration of gravity is 9.81 m/s 2 . Answer in units of m/s.

Answer 1

`v_(f)=-6.2 m/s`

Step-by-step explanation:

The ball will rise decreasing its speed until it reaches the highest point where its speed will be zero. From this point the tennis ball will begin to fall again, in the free fall the tennis ball will gain speed but now in the opposite direction. When it returns to the same point where it was launched, its speed will be the same as the one that was launched but with the opposite sign.

`v_(f)=-6.2 m/s`

We can check this using the equation:

`v_(f)^2=v_(i)^2+2gh`

where
`v_(i)=+6.2 m/s`

ang h is the height, but because the ball returns to the same point where it started, h =0

then

`v_(f)^2=v_(i)^2`

`v_(f)=v_(i)`

the initial and final velocity will be the same in number, but we know that the ball is going in the opposite direction, so the final velocity must have the opposite sign from the initial velocity

so if
`v_(i)=+6.2 m/s`,

`v_(f)=-6.2 m/s`