Question

The string of a simple pendulum is held horizontal at a height and then released. The tension in the string when the bob is at the lowest point is

• A. T = mg
• B. T = 20mg
• C. T = 3mg
• D. T = 4mg

Answer 1

The correct option is C

T = 3mg

If ‘ℓ’ is the length of the pendulum, the potential energy at highest point = kinetic energy at lowest point.

$mgl=\frac{1}{2}m{v}^2\Rightarrow v^2=2gl$

$\therefore T=mg+\frac{m{v}^2}{l}$ [$\because$ ‘T’ is centripetal force balancing the outward forces mg and $\frac{m{v}^2}{l}$]

$\Rightarrow$ T – mg + m(2g)

$\therefore$ T = 3mg