motion under gravity

The question talks about two bodies of same mass being dropped through the same height. To find the final velocity of the second body, we will find the value of acceleration from the first case.

 

Body 1. Initial velocity, u = 0

           Final velocity, v = 3 km/h

            Height, h

           Using v2 = u2 + 2ah

                    3² = 0 + 2ah

                    a  = 9/(2h)

 

Body 2. Initial velocity, u = 4 km/h

           Final velocity, v = ?

            Height, h

           Using v2 = u2 + 2ah

                    v² = 4² + 2ah

                    v² = 16 + 2(9/2h)h

                        = 25

                    v =  5 km/h