A man (mass = 50 kg) and his son (mass =20 kg) are standing on a frictionless surface facing each other. The man pushes his son so that he starts moving at a speed of 0.70 ms–1 with respect to the man. The speed of the man with respect to the surface is :
(1) 0.28 ms–1
(2) 0.47 ms–1
(3) 0.20 ms–1
(4) 0.14 ms–1
