Question

The bob of a pendulum is released from a horizontal position If the length of pendulum is 2 m, what is the speed with which the bob arrives at the lower most point. Assume that 10% of its energy is dissipated against air resistance:

(Take$g = 10 m s ^ { - 2 }$)

• A.
• B.
• C.
• D. $10 \mathrm {~ms} ^ { - 1 }$

Answer 1

Answer: (B)

Answer 2

The situation is as shown in the figure.

Potential energy of the bob at A = mgh

Kinetic energy of the bob at $\mathrm { B } = \frac { 1 } { 2 } \mathrm { mv } ^ { 2 }$

As 10% of the energy of the bob is dissipated against air resistance.

$\therefore \frac { 1 } { 2 } \mathrm { mv } ^ { 2 } = \frac { 90 } { 100 }$ of mgh or