Question

10. A boy of mass 55kg runs at 12m/s and hops on a 15kg skateboard that was at rest. What is thevelocity of the boy on the skateboard afterwards?

Answer 1

M = mass of the boy = 55kg

V = initial velocity of the boy = 12 m/s

m= mass of stationary skateboard = 15kg

v= velocity os stationary sketeboard= 0 m/s

V' = velocity of the boy on the skateboard after collision

Conservation of momentum:

MV + mv = (M + m) V'

Replacing:

55 kg * 12 m/s + 15 kg *0 = (55 kg+ 15 ) V'

Solve for V´'

660 = 70 V´'

660/70 = V'

V'= 9.42 m/s