Find the angle in radian through which a pendulum swings if its length is 75 cm and the tip describes an arc of length (i) 10 cm    (ii) 15 cm   (iii) 21 cm

Explanation

We know that in a circle of radius `r` unit, if an arc of length 1 unit subtends an angle `theta` radian at the centre, then `theta=frac{1}{r}`.


It is given that `r=75 cm`


(i) `1=10 cm`


`therefore theta=frac{10}{75}=frac{2}{15}` radian


(ii) `1=15 cm`


`therefore theta=frac{15}{75}=frac{1}{5}` radian


(iii) `1=21 cm`


`therefore theta=frac{21}{75}=frac{7}{25}` radian