What is the mass of a bullet if its kinetic energy is 720 J at a velocity of 400 m / s from the muzzle of a pistol?

These tasks: V (the speed of the considered bullet at the moment of departure from the muzzle of the pistol) = 400 m / s; Ek (kinetic energy) = 720 J.

We express the mass of the pistol bullet under consideration from the calculation formula for the kinetic energy: Ek = m * V ^ 2/2, whence m = 2 * Ek / V ^ 2.

Let’s calculate: m = 2 * 720/400 ^ 2 = 0.009 kg (9 g).

Answer: The mass of the pistol bullet in question is 9 g.