The Pebble Problem
note
Two identical twelve-inch rulers on a desk form an isosceles triangle with included angle θ. If Mickie moves the rulers so that θ increases at the rate of 2.5 radians per second, what is the rate of change of the area of the triangle when θ = π / 4 radians?
Note: the area of an isosceles triangle with legs of length l and included angle θ is given by the formula
A = 1/2l^2sin θ
127 square inches per second
Water is draining out of a conical tank at a constant rate of 120 cubic inches per minute. How fast is the level of water in the tank decreasing when there are 7 inches of water in the tank?
The level of water in the tank is decreasing at a rate of 3.1 inches per minute.
Farmer Bob’s square plot of land is slowly eroding away. Worried about the future of his farm, Farmer Bob measures the rate of erosion and finds that the length of each side of his square plot is decreasing at the constant rate of 2 feet / year. If he currently owns 250,000 square feet of land, what is the current rate of change of the area of Farmer Bob’s land?
Farmer Bob is losing 2,000 square feet of land per year.
A balloon is being inflated from a helium tank at a constant rate of 50 cubic inches per minute. How fast is the radius of the balloon increasing when the radius is 5 inches? Assume that the balloon is a perfect sphere.
1/2π inches per minute
Suppose that x and y are differentiable with respect to t. If x^3+y^3=9 and dy/dt=2, what is the value of dx/dt when y=1?
dx/dt=−1/2
A pebble is dropped into a pool of water, generating circular ripples. The radius of the largest ripple is increasing at a constant rate of 3 inches per second. By how many inches did the circumference of the ripple increase between 0 and 2 seconds?
12π in.