Question

On a frictionless horizontal air table, puck A (with mass 0.255 kg ) is moving toward puck B (with mass 0.375 kg ), which is initially at rest. After the collision, puck A has velocity 0.117 m/s to the left, and puck B has velocity 0.650 m/s to the right.

What was the speed vAi of puck A before the collision?

Calculate ΔK, the change in the total kinetic energy of the system that occurs during the collision.

Answer 1

Let us consider the right side direction as positive and the left side direction as negative.

Mass of puck A = m₁ = 0.255 kg

Mass of puck B = m₂ = 0.375 kg

Initial velocity of puck A = V₁

Initial velocity of puck B = V₂ = 0 m/s (At rest)

Velocity of puck A after the collision = V₃ = -0.117 m/s (Negative as it is directed to the left)

Velocity of puck B after the collision = V₄ = 0.65 m/s

By conservation of linear momentum,

V₁ = 0.839 m/s

Initial kinetic energy of the system = K₁

K₁ = 0.09 J

Final kinetic energy of the system = K₂

K₂ = 0.081 J

Change in total kinetic energy of the system = K

K = K₂ - K₁

K = 0.081 - 0.09

K = -0.009 J

a) Speed of puck A before the collision = 0.839 m/s

b) Change in total kinetic energy of the system during the collision = -0.009 J