12 Two small uniform discs A and B , of equal radius, have masses 3 kg and 5 kg respectively. The discs are sliding on a smooth horizontal surface and collide obliquely.
The contact between the discs is smooth and A is stationary after the collision.
Immediately before the collision B is moving with speed \(2 \mathrm {~ms} ^ { - 1 }\) in a direction making an angle of \(60 ^ { \circ }\) with the line of centres, XY (see diagram below).
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- Explain how you can tell that A must have been moving along XY before the collision.
The coefficient of restitution between A and B is 0.8 .
- - Determine the speed of A immediately before the collision.
- Determine the speed of B immediately after the collision.
- Determine the angle turned through by the direction of B in the collision.
Disc B subsequently collides with a smooth wall, which is parallel to XY. The kinetic energy of B after the collision with the wall is \(95 \%\) of the kinetic energy of B before the collision with the wall. - Determine the coefficient of restitution between B and the wall.