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Question:

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

Solution:

We know that in a circle of radius r unit, if an arc of length l unit subtends an angle θ radian at the centre, then θ = l/r.
It is given that r = 75cm
(i) l = 10cm ∴ θ = 10/75 = 2/15 radian
(ii) l = 15cm ∴ θ = 15/75 = 1/5 radian
(iii) l = 21cm ∴ θ = 21/75 = 7/25 radian