We consider two physical situations. In the first situation, we have a person st

Question

We consider two physical situations. In the first situation, we have a person starting from rest starting to run horizontally on earth. In the second situation, we have a person starting from rest and starting to swim in the water. The person who runs is in contact with the ground and the swimmer is in contact with the water. Which of the following are correct? A) The runner and the ground receive the same size momentum from their interaction. B) The runner receives a greater amount of momentum than the ground from their interaction. C) Earth receives a greater amount of moment than the runner from their interaction. D) The swimmer and the water receive the same size moment from their interaction. E) The swimmer receives a greater amount of momentum than the water from their interaction. F) The water receives a greater amount of momentum than the swimmer from their interaction. G) The runner and the ground receive equally kinetic energy from their interaction. H) The runner receives more kinetic energy than the Earth from their interaction. I) Earth receives more kinetic energy than the runner from their interaction. J) The swimmer and the water receive equally kinetic energy from their interaction. K) The swimmer receives more kinetic energy than the water from their interaction. L) The water receives more kinetic energy than the swimmer from their interaction.

Explanation / Answer

When we apply the law of conservation of momentum and energy for the runner and swimmer, what we can understand is that runner receives the momentum from earth and gains kinetic energy which makes him go. Energy comes from the runner/swimmer while the momentum.

So earth and water gain equal momentum as that of the runner and swimmer.

The KE is p2/2m. In this case, If we compare the magnitudes, the mass of earth is very very large compared to the mass of person so the kinetic energy can not be equal. so person will gain more amount of KE.

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