Two bodies of mass m and 4 m have equal kinetic energy. What is the ratio of their momentum?

When two bodies of masses m and 4m have the same amount of kinetic energy, their momenta differ because the relationship between kinetic energy and momentum is such that kinetic energy depends on both mass and the square of velocity, while momentum depends linearly on mass and velocity.

The velocity of a heavier body will have to be lower than that of a lighter body in order to have the same kinetic energy. For the kinetic energy being constant, the momentum of a body varies directly as the square root of its mass. So when their momenta are compared, the ratio of the momenta is equal to the square root of the ratio of the masses.

In this case, the first body has mass m, while the second has a mass of 4m. The square root of their mass ratio, √1} : √4, gives the momentum ratio as 1:2. This means the body with four times the mass has double the momentum of the lighter body under equal kinetic energy conditions.

Hence, the kinetic energy of both bodies is the same, but their momentum differs because of the mass in these bodies. It is greater in the former body compared with the later.

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