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

Answer 1

The correct option is C $800J$

Formulae,

$M_1{V}_1=(M_1+M_2)V$

$\therefore V=\frac{M_1{V}_1}{M_1+M_2}$

$=\frac{20\times 5}{20+5}=4$

$KE=\frac{1}{2}(M_1+M_2)V^2$

$=\frac{1}{2}(20+5)4^2$

$=200J$