A cue ball with mass 170g hits a stationary number 8 ball, which has mass 160g. The cue ball
and the 8 ball move with a speed of 0.2m/s and 0.3m/s respectively after the collision. What
was the speed of the cue ball before the collision?

0.49 m/s

Explanation:

The law of conservation of linear momentum states that the sum of momentum in a system before and after collision are same. Momentum is a product of mass and velocity of an object hence in this case

Where m represent mass, u and v represent the initial and final velocities respectively, subscripts c and 8 represent cue ball and number 8 ball respectively.

Since number 8 ball is initially at rest, its initial velocity is zero. Replacing mass of cue ball with 170 g while mass of number 8 ball with 160g, then taking final velocity of cue ball as 0.2 m/s and final velocity of 8 ball as 0.3 m/s then we get

a and c

c is 100% but i am confused in a