Question

Two solid cylinder with radii 5cm and 10cm and length 7cm and 5cm respectively are melted and recast into a cylindrical disc of thickness 3cm. Calculate the radius

Answer 1

15 centimeters.

Explanation:

We must calculate the volume of each cylinder and add it, like this:

v = pi * (r ^ 2) * l

replacing:

v1 = 3.14 * (5 ^ 2) * 7

v1 = 549.5

v2 = 3.14 * (10 ^ 2) * 5

v2 = 1570

The sum would be:

549.5 + 1570 = 2119.5

That would be the volume of the cylindrical disk, this case would be the same formula only that it would not be length but thickness, like this:

v = pi * (r ^ 2) * t

we want to know r, therefore:

r ^ 2 = v / pi * t

replacing:

r ^ 2 = 2119.5 / (3.14 * 3)

r ^ 2 = 225

r = 15

which means that the radius would be 15 centimeters.