# Sample Problem Kinetic Energy And Work

Sample Problem Kinetic Energy And Work

A package of spicy Cajun pralines lies on a friction less floor, attached to the free end of a spring in the arrangement.An applied force of magnitude.

(a) How much work does the spring force do on the package if the package is pulled rightward from 17 mm?

SOLUTION: A Key Idea here is that as the package moves from one position to another, the spring force does work .

We can probably find Hooke’s law, but we need a second Key Idea to use it: Were the package held stationary, the spring force would have to balance the applied. (b) Next, the package is moved leftward to X = -12 mm. How much work does the spring force no on the package during this displacement? Explain the sign of this work.

SOLUTION: The Key Idea here is the first one we noted in part (a). Now X = +17 mm and x = -12 mm, and yields. This work done on the block by the spring force is positive because the spring force does more positive work as the block moves from Xi = + 17 mm to the spring’s relaxed position.