Question

A mass of $20kg$ moving with a speed of $10m/s$ collides with another stationary mass of $5kg$. As a result of the collision, the two masses stick together. The kinetic energy of the composite mass will be

• A. 600 J
• B. 800 J
• C. 1000 J
• D. 1200 J

Answer 1

Answer: (B)

Given, $m_1=20kg,u_1=10m/s$,
Using law of conservation of momentum,
$m_1{u}_1+m_2{u}_2=\left(m_1+m_2\right)v20\times 10+5\times 0=(20+5)\times v$
$\therefore v=\frac{200}{25}=8m/s$
Kinetic energy of the composite mass
$=\frac{1}{2}\left(m_1+m_2\right)v^2$
$=\frac{1}{2}(20+5)\times (8{)}^2$
$=25\times 32=800J$