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Physics Question on work, energy and power

A man (mass = 50 kg50\, kg) and his son (mass = 20 kg20\, 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−10.70\, ms^{-1} with respect to the man. The speed of the man with respect to the surface is :

A

0.20 ms−10.20\, ms ^{-1}

B

0.14 ms−10.14\, ms ^{-1}

C

0.47 ms−10.47\, ms ^{-1}

D

0.28 ms−10.28\, ms ^{-1}

Answer

0.20 ms−10.20\, ms ^{-1}

Explanation

Solution

⇒0=50V1−20V2\Rightarrow 0=50 V_{1} - 20V_{2} and V1+V2=0.7V_{1} + V_{2} = 0.7
⇒V1=0.2\Rightarrow V_{1} = 0.2