JEE Main Physics question
A machine which is 75% efficient, uses 12 J of energy in lifting up a 1 kg mass through a certain distance. The mass is then allowed to fall through that distance. The velocity of the ball at the end of its fall is
Answer: (C)
Solution
Useful energy (converted to PE) = 0.75×12 = 9 J. On falling, this all converts to KE: ½(1)v² = 9 ⟹ v² = 18 ⟹ v = √18 ms⁻¹.