Question

A block is placed on the top of a smooth inclined plane of inclination $\theta$ kept on the floor of a lift. When the lift is descending with a retardation $a$, the block is released. The acceleration of the block relative to the incline is

• A. $\text{g sin}\theta$
• B. $\text{a sin}\theta$
• C. $(g-a)\text{sin}\theta$
• D. $(g+a)\text{sin}\theta$

Answer 1

The correct option is D $(g+a)\text{sin}\theta$

Lift is descending with retardation. Therefore acceleration a is upwards or pseudo force ma is upwards. Relative to lift force in downward diretion is m(g + a) in plane of mg. Therefore in smooth plane acceleration will be $(g+a)\text{sin}\theta$ not $\text{g sin}\theta .$