JEE Main 2022 · 29 June · evening · Single correct · +4 / −1
In the given figure, the block of mass m is dropped from the point 'A'. The expression for kinetic energy of block when it reaches point 'B' is
- (a) 1/2mg y₀²
- (b) 1/2mg y²
- (c) mg(y - y₀)
- (d) mgy₀
Answer and solution
Answer (d) mgy₀
Solution
Physics sir · 3 steps
Kinetic energy gained equals potential energy lost, and the block falls only y₀ from A to B.
- Read the figure. Point A is at height y above the ground. Point B is y₀ below A, so B is at height y - y₀. The block starts from rest at A, so its kinetic energy at A is zero.
- Energy conservation. Only gravity does work, so the loss in potential energy from A to B becomes kinetic energy at B.
K_B = mg y - mg (y - y₀) = mg y₀
- So. The kinetic energy at B is mg y₀, which is option (d).
The idea to keep. Kinetic energy after a fall depends only on the height actually fallen, not on where you put the zero of potential energy. Always measure the drop between the two points.
Answer from the NTA final answer key. Solution by PrepWiser.