Question

A metal ball of mass 2 kg moving with speed of 36 km/hr is having a collision with a stationary ball of mass 3 kg. If after collision, both the balls move together, the loss in kinetic energy due to collision is :

• A. $80J$
• B. $40J$
• C. $60J$
• D. $160J$

Answer 1

Answer: (C)

$60J$

Let v be the common velocity.
Applying conservation of momentum
$2\times 10+3\times 0=(2+3)v$
$v=\frac{10\times 2}{5}=4m/sec$
$[36km/hour=10m/sec]$
Initial Energy $=\frac{1}{2}\times 2\times {\left(10\right)}^2+0=100J$
Final Energy $=\frac{1}{2}\times 5\times 4\times 4=40J$
Loss of energy $=100-40=60$ joule