Question

Find the number of coins of 1.5 cm diameter and 0.2 cm thickness to be melted to form a right circular cylinder of height 10 cm and diameter 4.5 cm.

Answer 1

Here, as the coins are melted into the form of a right circular cylinder, so we have to divide the volume of cylinder by the volume of coins.

Diameter=1.5 cm

So radius=1.5/2

=0.75 cm

Thickness (height)=0.2 cm

So, volume of coins=πr^2h

=π×0.75^2×0.2

=9π/80 cm^3


Now, diameter of cylinder=4.5 cm

So radius=4.5/2 cm

=2.25 cm

Height=10 cm

So its volume=πr^2h

=π×2.25^2×10

=405π/8 cm^3

Now,number of coins =405π/8÷9π/80

=450