Question

a man throws a ball vertically upwards with a velocity of 20 m /s-2 . After what time will the ball come back to his hands​

Answer 1

The ball will reach in 4 seconds

Answer 2

Explanation:

A man threw a ball vertical upwards with a velocity of 20 m/s. After what time will the ball come back to his hands

Vfinal=Vinitial−gtVfinal=Vinitial−gt 

The velocity of the ball as it hits the man's hands, assuming they're at the same height, will be -20m/s, the opposite of its original velocity, so you put that in for the final velocity.

==>−20m/s=20m/s−9.8m/s2t−20m/s=20m/s−9.8m/s2t 

==>−40m/s−9.8m/s2=t−40m/s−9.8m/s2=t 

t=4.082Sec, t=4.082Sec

There's no need to calculate the time it takes to reach its peak then multiply that by 2 like the other responses suggest.

That just adds another step, however it works all the same.

With this equation you can determine the velocity at any time, or any time with a given velocity.

This does not factor in wind resistance.