A 50 kg man floats in gravity-free space 10 m above a floor. He throws $a_0.5$ kg stone downward at speed 2 m s⁻¹ relative to him. On reaching the floor, how high is the man above it?
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Question

A 50 kg man floats in gravity-free space 10 m above a floor. He throws a 0.5 kg stone downward at speed 2 m s⁻¹ relative to him. On reaching the floor, how high is the man above it?

G1 Physics · Accepted Answer

Stone reaches the floor in approximately 10/2=5 s. Momentum conservation gives upward recoil speed to the man ≈(0.5×2)/50=0.02 m s⁻¹. In 5 s he rises another 0.02×5=0.1 m. Distance from floor =10.1 m. Answer: B.