Question

A ball is thrown vertically upwards from the ground and it reaches a height of 20m. Calculate
the speed the ball had when it was launched.

I don't know how to solve this due to the fact that in the problem we only have the height as data , not even mass.

Answer 1

the kinetic energy of the ball at launch equals the gravitational potential energy at the peak

½ m v² = m g h

v = √(2 g h) = √(2 * 9.8 * 20) m/s

Answer 2

But wait oh did you get the mass?