# A ball with a mass of 7 kg moving at 1 m/s hits a still ball with a mass of 10 kg. If the first ball stops moving, how fast is the second ball moving? How much kinetic energy was lost as heat in the collision?

Nov 2, 2016

By momentum conservation ,

${P}_{i} = {P}_{f}$------[where $P = m o m e n t u m = m a s s \times v e l o c i t y$]

Let the velocity of ball with mass 10 kg be 'v'.

$7 \times 1 + 10 \times 0 = 7 \times 0 + 10 \times v$

$7 = 10 v$

$v = \frac{7}{10}$

$v = 0.7 \frac{m}{s}$

Loss in kinetic energy = KE_i - KE_f#

Loss in kinetic energy = $\frac{1}{2} \times 7 \times 1 - \frac{1}{2} \times 10 \times 0.7 \times 0.7$

Loss in kinetic energy = $\frac{7}{2} - \frac{49}{20}$

Loss in kinetic energy = $\frac{21}{20}$ Joule