Question

A pendulum of mass 'm' is pulled from position 'A' by applying a constant horizontal force F = mg/3. Velocity at point 'B' shown in figure –

• A. $\sqrt { \frac { 2 \ell \mathrm { g } } { 3 } }$
• B. $\sqrt { \frac { 3 \ell \mathrm { g } } { 5 } }$
• C. $\sqrt { \frac { 4 } { 5 } \ell g }$
• D. Zero

Answer 1

Answer: (D)

Zero

Answer 2

W_net = DK

̃ F sin q.l – mg l (1 – cos q) = $\frac { 1 } { 2 } \mathrm { mv } ^ { 2 }$

(\ q = 37⁰ and F = $\frac { \mathrm { mg } } { 3 }$ )

̃ v = $\left\{ \frac { 2 l } { 5 \mathrm {~m} } ( 3 \mathrm {~F} - \mathrm { mg } ) \right\} ^ { 1 / 2 }$ = 0