Question

A body of mass 2 kg moving with velocity of 6 m/s strike another body of same mass at rest and sticks to it. The amount of heat evolved during collision is:

• A. 18 J
• B. 36 J
• C. 9 J
• D. 3 J

Answer 1

The correct option is A 18 J

Given,

Mass of the moving body $m_1=2kg$

Velocity of the body $v_1=6m/s$,

Mass of another body $m_2=2kg$

Velocity of the another body $v_2=0m/s$

As per the conservation of the momentum,

Common velocity, $v=\frac{m_1{v}_1+m_2{v}_2}{m_1+m_2}$
$=\frac{2\times 0+2\times 0}{2+2}=3m/s$
Initial kinetic energy $\left(E_1\right)$
$=\frac{1}{2}{m}_1{v}_1^2+\frac{1}{2}{m}_2{v}_2^2=\frac{1}{2}\times 2\times (6{)}^2=36J$

Energy of the body, after collision is
$=\frac{1}{2}(m_1+m_2)V^2=\frac{1}{2}(2+2)(3{)}^2=18J$

So, As per the conservation of the energy,

"Energy neither can be produce nor can be destroy,it transform from one form to another form."

So, Energy transformed to the heat

$\therefore$ Heat evolved $=(36-18)J=18J$