Question

Question 2 O out of 3 points A 2.5 kg ball moving at 4.2 m/s collides with a 2.5 kg stationary ball in a perfectly elastic collision. What is the velocity of the second ball after the collision? Selected Answer: 4.2 m/s Answers: 4.2 m/s None of these 8.4 ms 1.2 m/s 4.8 m/s

Answer 1

4.2 m/s

you have given the right answer.

In a perfectly elastic collision, the total momentum, as well as the total kinetic energy, is conserved. Whereas in inelastic collision momentum is conserved but the kinetic energy is not conserved.

m1u1 + m2u2 = m1v1 + m2v2

In perfectly elastic collision when the masses of the two bodies are same (m1 = m2) then u1 = v2 and u2 = v1

therefore, m1 = m2 = 2.5Kg and u2 = v1 = 0

m1u1 + m2u2 = m1v1 + m2v2

2.5(4.2) + 2.5(0) = 2.5(0) + 2.5(v2)

v2 = 4.2m/s