A ball of mass m1 moving with speed u along a straight, frictionless surface collides perfectly elastically and head-on with another ball of mass m2 that is initially at rest. Under which condition will the first ball reverse its direction of motion after the collision?
a) m1>m2
b) m1<m2
c) m1=m2
d) The direction of motion of the first ball after collision is independent of the mass ratio