Question

With what speed a ball must be thrown upwards if it reaches thrower hands in 5s

Answer 1

We can use Kinematic equations for that

We know that the speed we throw a ball upwards will be the exact speed it comes back down. So If i throw a ball at 5 m/s, it will come back to me at -5m/s assuming no air resistance.

vf = Final velocity

vi = Initial velocity

So in this case, its safe to assume that vf = vi

Vf = vi + at

Vf will be the negative vi

There fore

-vi = vi + at

Solving for vi gives us at/-2

We know the acceleration and we know the time

vi = at/-2

vi = (-9.8)(5)/-2 = 24.5 m/s

So we need to throw the ball at 24.5 m/s