# 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 $0.70ms^{-1}$ with respect to the man. The speed of the man with respect to the surface is : Option 1) $0.47ms^{-1}$ Option 2) $0.14ms^{-1}$ Option 3) $0.28ms^{-1}$ Option 4) $0.20ms^{-1}$

$\Rightarrow 0=50v_{1}-20v_{2}$

and also $v_{1}+v_{2}=0.7$

$\Rightarrow v_{1}=0.2m/s$

Option 1)

$0.47ms^{-1}$

Option 2)

$0.14ms^{-1}$

Option 3)

$0.28ms^{-1}$

Option 4)

$0.20ms^{-1}$

Option 4

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