Question

A flat car of mass $m_0$ starts moving to the right due to a constant horizontal force F at t =0. Sand spills on the flat car from a stationary hopper. The velocity of loading is constant and is equal to $\mu$ kg s${}^{-1}$. Then,

• A. kinetic energy of loaded car, at an instant, is less than the work done by the force F (up to that instant).
• B. kinetic energy of loaded car at an instant is equal to work done by force F up to that instant.
• C. Momentum of loaded car at an instant is less than impulse of force F up to that instant.
• D. None of these.

Answer 1

The correct option is B kinetic energy of loaded car at an instant is equal to work done by force F up to that instant.

We see that the only force doing work in the direction of motion that is along X is the force. And from the work energy theorem, total work done is equal to change in kinetic energy.

Hence. KE of loaded car at any instant is equal to work done by force F till that instant.

Answer-(B)