Question

A simple pendulum is released from A as shown in figure. If 10 g and 100 cm represent the mass of the bob and length of the pendulum. what is the gain in K.E. at B? (g = 10 m/s²) 

(A) 0.5 J 

(B) 5 × 10^–2 J 

(C) 5 J 

(D) 0.5 × 10^–3 J

Answer 1

Correct option: (B) 5 × 10^–2 J

Explanation:

Loss in PE = gain in KE

∴ Gain in KE = mgh

= {(10) / (1000)} × 10 × h

= (h / 10)

cos 60 = (h/ℓ)

h = cos 60 (ℓ)

= (1/2) × 1 = (1/2)m

Gain in KE = (h / 10) = (1 / 20) J

= 5 × 10^–2 J