Inverse Variation

Question

The speed of the water in a whirlpool varies inversely with the radius. If the water speed is 2.5 feet per second at a radius of 30 feet, what is the speed of the water at a radius of 3 feet?

Answer 1

v₁ = 2.5 ft/s

r₁ = 30 ft

v₂ = ? ft/s

r₂ = 3 ft

The product of speed v and radius r is constant.

v₁r₁ = v₂r₂

Solve for v₂.

v₂ = v₁r₁ / r₂

Plug in the values and get v₂ in ft/s.