A smooth sphere P, of mass m kg, moving with speed 5u m/s collides directly with a smooth sphere Q, of mass 2m kg, moving towards each other with speed 2u m/s.

The coefficient of restitution between the spheres is e.

find the condition satisfied by e if the 2 spheres move in the same direction after the collision.

using the 2 normal equations i got their final speeds to be 3u-2ue and 3u-ue

because they move in the same direction i let 3u-2ue >0 and 3u-ue>0

solving these i get e<3 and e>3/2

the answer at the back of the book is e<1/14

i can go though my answer in more detail if you need it

thanks