Question

b) A boy of mass 30 kg jumps with a horizontal velocity of 6 m/s onto a stationary cart
with frictionless wheels. The mass of the cart is 6kg. What is his velocity as the cart starts
moving? Assume that there is no external unbalanced force working in horizontal
direction.

Answer 1

Answer: His velocity as cart starts moving, V = 5m/s

Explanation: As External force in horizontal direction = 0, by momentum conservation.

Let's assume the velocity of the system after the boy jumps on the cart is V.

                    Initial momentum = final momentum

                    mass of boy*velocity of boy = (mass of boy + mass of cart)*velocity of the  system

                    30kg × 6m/s = (30kg+6kg) × V

                                       V = 5 m/s