NEET 2021 · PhysicsWork donePrevious Year Question
A particle is released from rest at height S above the earth's surface. At a certain height its kinetic energy is three times its potential energy (taking the surface as reference). The height above the surface and the speed at that instant are respectively:
Answer: (B) S/4 and √(3gS/2). Correct Answer (B): S/4 and √(3gS/2) Solution: Energy conservation (near surface): mgS = KE + PE = 3PE + PE = 4PE ⇒ PE = mgS/4 ⇒ h = S/4.
- A.3S/4 and √(3gS/2)
- B.S/4 and √(3gS/2)✓
- C.S/2 and √(3gS/2)
- D.S/4 and √(3gS)
Correct Answer
(B) S/4 and √(3gS/2)
Solution & Explanation
Correct Answer (B): S/4 and √(3gS/2) Solution: Energy conservation (near surface): mgS = KE + PE = 3PE + PE = 4PE ⇒ PE = mgS/4 ⇒ h = S/4. KE = 3mgS/4 = ½mv² ⇒ v = √(3gS/2).
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