A man of mass 50 kg starts moving on the earth and acquires a speed of 1.8 m/s. With what speed does the earth recoil? Mass of earth = 6 × 1024 kg.

Mass of man, m1 = 50 kg

Mass of earth, m2 = 6×1024 kg


Speed of man, v1 = 1.8 m/s


Speed of earth = v2


Applying conservation of momentum, m1v1 = m2v2


50×1.8 = 6×1024×v2


v2 = 1.5×10-23 m/s


Speed at which earth recoils = 1.5×1024 m/s


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