The weight of a synthetic ball varies directly with the cube of its radius.

Question

A ball with a radius of 2 inches weighs 1.20 pounds. Find the weight of a ball of the same material with a 3-inch radius.

Answer 1

W = k*R^3

1.2 = k*{2^3)

1.2/8 = k

0.15 = k

W = 0.15*R^3

So then W = 0.15 * 3^3 = 0.15*27 = 4.05