Cart A, with a mass of 0.4 kg, travels on a horizontal air track at 6 m/s and hits cart B, which has a mass of 0.8 kg and is initially at rest. After the collision, cart A has a velocity of 2 m/s in the opposite direction. What is the final kinetic energy of cart B

6.4 J

Explanation:

For cart A

mA = 0.4 kg, uA = 6 m/s, vA = - 2 m/s

For cart B

mB = 0.8 kg, uB = 0, vB = ?

use the law of conservation of momentum

momentum of system before coliision = momentum of system after collision

mA uA + mB uB = mA vA + mB vB

0.4 x 6 + 0 = 0.4 x ( - 2) + 0.8 x vB

vB = 4 m/s

Kinetic energy of Cart B after collision = 1/2 mB vB^2

= 1/2 x 0.8 x 4 x 4 = 6.4 J