quick question about coeffecient of restitution

A smooth sphere P of mass m is moving in a straight line with speed U on a smooth horizontal table. Another smooth sphere Q of mass 2m is at rest on the table. The sphere P collides directly with Q. After the collision the direction of motion of P is unchanged. The spheres have the same radii and the coefficient of restitution between P and Q is e. By modelling the spheres as particles,

(a) show that the speed of Q immediately after the collision is 1/3(1 + e)U
Which ive done.

(b) find the range of possible values of e. but im not too sure how u do this?

any ideas please?

oh ok i get it now, thanks. one more question:

A rocket R of mass 100 kg is projected from a point A with speed 80ms^-1 at an angle of elevation of 60°. The point A is 20 m vertically above a point O which is on horizontal ground. The rocket R moves freely under gravity. At B the velocity of R is horizontal. By modelling R as a particle,

find (a) the height in m of B above the ground,

(b) the time taken for R to reach B from A.

When R is at B, there is an internal explosion and R breaks into two parts P and Q of masses 60 kg and 40 kg respectively. Immediately after the explosion the velocity of P is 80ms^-1 horizontally away from A. After the explosion the paths of P and Q remain in the plane OAB. Part Q strikes the ground at C. By modelling P and Q as particles,

(c) show that the speed of Q immediately after the explosion is 20ms^-1

(d) find the distance OC.

thanks a lot.