1.1. Ball X has a mass of 50 g and is supported by a long string, as shown in Fig. 1.1.

Fig. 1.1

The ball is pulled back and released. The ball collides normally with a flat surface at a velocity of 4.5 m s⁻¹ and rebounds elastically.

The positive direction is horizontal and to the right.

Determine the total change in momentum of ball X. 

1.2. Ball X is hung next to ball Y which is supported by a string of the same length, as shown in Fig. 1.2.

Fig. 1.2

Ball Y has a mass of 125 g.

The balls are each pulled back and pushed towards each other. When the balls collide, the strings are vertical. The balls rebound in opposite directions.

The velocities of X and Y just before and just after the collision are shown in Fig. 1.2.

Use the conservation of linear momentum to determine the rebound velocity $v$ of Y.

1.3. Deduce whether the collision in (b) is elastic or inelastic.

1.4. Use Newton’s laws to explain why the magnitude of the change in momentum of each ball is the same.