The energy stores in a stretched spring depends on the distance x that it has been stretched according to the equation E=1/2kx^2 where k is a constant that depends on how stiff the spring is. Suppose that for a certain spring, k = 0.20. This spring is being stretched at a rate of 1.5 cm/sec. How quickly is the energy stored in the spring increasing at the moment that the spring has been stretched x = 10 cm?

• A. 3.0 joules per second
• B. 3.5 joules per second
• C. 4.0 joules per second
• D. 4.5 joules per second