question_answer

          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 \[0.70\,m{{s}^{-1}}\] with respect to the man. The speed of the man with respect to the surface is :                      [JEE Main Held on 12-4-2019 Morning]

A) \[0.20\,m{{s}^{-1}}\]

B) \[0.14\,m{{s}^{-1}}\]

C) \[0.47\,m{{s}^{-1}}\]                      

D) \[0.28\,m{{s}^{-1}}\]

Correct Answer: A

Solution :

            \[\Rightarrow 0=50{{V}_{1}}-20{{V}_{2}}\]and\[{{V}_{1}}+{{V}_{2}}=0.7\]\[\Rightarrow {{V}_{1}}=0.2\]