As shown in the diagram,
Consider a circle with centre O and AOB being the sector with sector angle θ and arc APB.
Length of the arc of a sector of angle θ, S
1.If the angular diameter of the moon be 30′, how far from the eye a coin of diameter 2.2 cm be kept to hide the moon?
θ = 30′ =0.50
S= 2.2 cm
r= (2.2*360)/(2*3.14*0.5)cm= 252 cm