Question

A pendulum of length 200 cm is horizontal when its bob of mass 200 gm is released. It has 90% of initial energy when the bob reaches the lower most point. Speed of the bob at this point is –

• A. 8 m/s
• B. 4.5 m/s
• C. 5 m/s
• D. 6 m/s

Answer 1

Answer: (D)

6 m/s

Answer 2

v = $\sqrt{2gh}$ when 100% energy gets converted.

But here $\frac{1}{2}$ mv² = 0.9 mgh

i.e. v = $\sqrt{1.8gh}$ Ž v = $\sqrt{1.8 \times 10 \times 2}$ = 6 m/s