Question

A body of mass $2 \,kg$ moving with velocity of $6\, m/s$ strikes in elastically with another body of same mass mass at rest. The amount of heat evolved during collision is

• A. 18 J
• B. 36 J
• C. 9 J
• D. 3 J

Answer 1

Answer: (A)

18 J

Answer 2

Common velocity, $v =\frac{m_{1} v_{1}+m_{2} v_{2}}{m_{1}+m_{2}}$
$=\frac{2 \times 6 \times+2 \times 0}{2+2}=3 \,m / s$
Initial kinetic energy $\left(E_{1}\right)$
$=\frac{1}{2} m_{1} v_{1}^{2}+\frac{1}{2} m_{2} v_{2}^{2}$
$=\frac{1}{2} \times 2 \times(6)^{2}=36 J$
$=\frac{1}{2}\left(m_{1}+m_{2}\right) V^{2}$
$=\frac{1}{2}(2+2)(3)^{2}=18\, J$
So, the amount of heat evolved
$=(36-18) J =18 \,J$

Therefore, the correct option is (A): 18 J