Posted by rachel on .
water is poured into a conical paper cup so that the height increases at the constant rate of 1 inch per second. if the cup is 6 inches tall and its top has a radius of 2 inches, how fast is the volume of water in the cup increasing when the height is 3 inches?
Make a diagram, and label the radius of the water level r, and the height of the water h
V = (1/3)πr^2h
but by ratios, r/h = 2/6 = 1/3
then r= h/3
V = (1/3)π(h^2/9)(h) = (π/27)h^3
dV/dt = (π/9)h^2 dh/dt
= (π/9)(3^2) (1) = π cubic inches/sec
check my arithmetic