Question

Q 65. The length of a pendulum is 60 cm. The angle through which it swings when its tip
describes an arc of length 16.5 cm will be
​

Answer 1

length of pendulum = radius of circle, r = 60cm

a/c to question, we have to find angle through which it swings when its tip describes an arc of length 16.5cm.

so, arc length , l = 16.5 cm

let subtended angle = α.

use formula, $\boxed{\bf{\theta=\frac{l}{r}}}$

so, $\theta=\alpha$ , l = 16.5cm

and r = 60cm

so, α = 16.5/60 = 3.3/12 = 1.1/4 = 11/40 rad

we know, π rad = 180°

so, 1 rad = (180/π)°

so, 11/40 rad =[ (180/π) × 11/40 ]°

= 180/(22/7) × 11/40

= 180 × 7/22 × 11/40

= 9 × 7/4

= 63/4 = 15° (3/4 × 60)' [ we know, 1° = 60']

= 15° 45'

Therefore the angle through which pendulum swings is 15° 45'