# A ball with a mass of 9 kg moving at 14 m/s hits a still ball with a mass of 18 kg. If the first ball stops moving, how fast is the second ball moving?

If the second ball is in rest before collision then after collision velocity of the second ball is 7m/s.

Dec 23, 2015

$7$ $m$/$s$

#### Explanation:

${M}_{1}$= mass of first ball, ${V}_{1}$= velocity of first ball
${M}_{2}$= mass of second ball, ${V}_{2}$= velocity of second ball

by conservation of linear momentum

${M}_{1} {V}_{1} + {M}_{2} {V}_{2} = {M}_{1} {V}_{1} + {M}_{2} {V}_{2}$

9 x 14 + 18 x 0 = 9 x 0 + 18 x ${V}_{2}$

therefore ${V}_{2}$ = $\frac{9 \text{ x } 14}{18}$ = $7$ $m$/$s$