JEE Main 2019 Physics question
A person of mass M is sitting on a swing of length L and swinging with an angular amplitude . If the person stands up when the swing passes through its lowest point, the work done by him, assuming that his center of mass moves by a distance ℓ (ℓ << L), is close to:
Answer: (A)
Solution
Angular momentum is conserved: v′ = vL/(L − ℓ); W = mgℓ + ½m(v′ − v) ≈ mgℓ + mvℓ/L = mgℓ(1 + θ).