A smooth sphere of mass 'M' moving with velocity 'u' directly collides elastically with another sphere of mass 'm' at rest. After collision their final velocities are 'V' and 'v' respectively. The value of 'v' is
v2=(m2−m1m1+m2)u2+2m1u1m1+m2=2MuM+m=2u1+mM