Question

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

• A. 36 J
• B. 18 J
• C. 9 J
• D. 3 J

Answer 1

Answer: (B)

Common velocity $=\frac{m_1{v}_1+m_2{v}_2}{m_1+m_2}$ $=\frac{2\times 6+2\times 0}{2+2}$ $=3m\text{/}s$ Initial kinetic energy $=\frac{1}{2}{m}_1{v}_1^2+\frac{1}{2}{m}_2{v}_2^2$ $=\frac{1}{2}\times 2\times {(6)}^2$ = 36 J Final kinetic energy $=\frac{1}{2}(m_1+m_2)v^2$ $=\frac{1}{2}(2+2){(3)}^2=18J$ The amount of heat evolved $=E_1-E_2$ = 36 ? 18 = 18J