Question

A cart of mass $50\text{kg}$ is moving on a straight track with a speed of $12\text{m/s}$. A mass of $10\text{kg}$ is gently put into the cart. What will be the velocity of the cart after this?

• A. $12\text{m/s}$
• B. $10\text{m/s}$
• C. $14\text{m/s}$
• D. $16\text{m/s}$

Answer 1

The correct option is B $10\text{m/s}$

Initial momentum of the cart,

$P_i=mu=50\times 12=600\text{kg-m/s}$

Now, after gently putting the mass of $10\text{kg}$ into the cart, let the speed of the cart be $v$.

Final momentum of the cart,

$P_f=Mv=(50+10)\times v=60v\text{kg-m/s}$

Since, there is no external force, its momentum is conserved.

$\therefore P_i=P_f$

$\Rightarrow 600=60v$

$\Rightarrow v=10\text{m/s}$