Question

A block of mass 1 kg moving with a speed of $2{ms}^{-1}$ collides with and sticks to another block of mass 2 kg which was initially at rest. After the collision

• A. The momentum of the system is less than $2{kgms}^{-1}$
• B. The kinetic energy of the system is $\frac{2}{3}J$
• C. The kinetic energy of the system is $2J$
• D. None of these

Answer 1

The correct option is B The kinetic energy of the system is $\frac{2}{3}J$

Option (a) can not be true as momentum has to remain conserved.
Common velocity, $\upsilon =\frac{m_1{\upsilon }_1+m_2{\upsilon }_2}{m_1+m_2}=\frac{2}{3}$
kinetic energy of the system'after collision
$=\frac{1}{2}(m_1+m_2){\upsilon }^2=\frac{1}{2}\left(3\right)\times \frac{4}{9}=\frac{2}{3}$