Question

A 10 kg ball moving with velocity $2 ms^{-1}$ collides with a 20 kg mass initially at rest. If both of them coalesce, the final velocity of combined mass is

• A. $\frac{3}{4} ms^{-1}$
• B. $\frac{1}{3} ms^{-1}$
• C. $\frac{3}{2} ms^{-1}$
• D. $\frac{2}{3} ms^{-1}$

Answer 1

Answer: (D)

Using law of conservation of momentum
$m_1u_1+m_2u_2=(m_1+m_2)v$
Here ,$m_1=10 kg ,m_2 =20 kg ,u_1=2 ms^{-1},u=0$
= 10 $\times 2 +0= (10+20)v$
or $v=\frac{20}{30}=\frac{2}{3}ms^{-1}$