Two carts move along the same straight, frictionless track in opposite directions. Cart X of mass 3kg has speed 4m s−1 to the right, while cart Y of mass 1kg has speed 2m s−1 to the left. They collide head-on and the collision is perfectly elastic. By what percentage does the kinetic energy of cart Y change as a result of the collision?
a) 0%
b) 525%increase
c) 1125%increase
d) 1225%increase