Object A of mass 0.70 kg travels horizontally on a frictionless surface at 20 m/s. It collides with object B, which is initially stationary and rebounds with 70% of its initial kinetic energy. What is the magnitude of the change in momentum of object A?

25.71 kgm/s

Explanation:

Let K₁ and K₂ be the initial and final kinetic energies of object A and v₁ and v₂ its initial and final speeds.

Given that K₂ = 0.7K₁

1/2mv₂² = 0.7 (1/2mv₁²)

v₂ = √0.7v₁ = √0.7 * 20 m/s = ±16.73 m/s

Since A rebounds, its velocity = - 16.73 m/s and its momentum change, p₂ = mΔv = m (v₂ - v₁) = 0.7 kg (-16.73 - 20) m/s = 0.7 (-36.73) = - 25.71 kgm/s.

Th magnitude of object A's momentum change is thus 25.71 kgm/s