Q. A pendulum of length $2m$ lift at $P.$ When it reaches $Q,$ it losses 10% of its total energy due to air resistance. The velocity at $Q$ is
A) $6\ m/s$
B) $1\ m/s$
C) $2\ m/s$
D) $8\ m/s$
Explanation
(a) If $v$ is velocity of pendulum at $Q$
and 10% energy is lost while moving from $P$ to $Q$
Hence, by applying conservation of energy between $P$ and $Q$
$\frac{1}{2}mv^{2} = 0.9\ (mgh) \Rightarrow v^{2} = 2 \times 0.9 \times 10 \times 2 \Rightarrow v = 6m/s$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.