Question

A horizontal plane supports a plank with a block placed on it. A light elastic string is attached to the block, which is attached to a fixed point O. Initially, the cord is unstretched and vertical. The plank is slowly shifted to the right until the block starts sliding over it. It occurs at the moment when the cord deviants from vertical by an angle $\theta =0^0$. Work done by the force F equals

• A. Energy lot against friction $F_1$ plus strain energy in cord.
• B. Work done against total friction acting on the plank alone.
• C. Work done against total friction acting on the plank plus strain energy in the cord.
• D. Work done against total friction acting on the plank plus strain energy in the cord minus work done by friction acting on the block.

Answer 1

Answer: (A), (B), (D)

The correct options are
A Energy lot against friction $F_1$ plus strain energy in cord.
B Work done against total friction acting on the plank alone.
D Work done against total friction acting on the plank plus strain energy in the cord minus work done by friction acting on the block.