In Example 1, find the work done in stretching the spring from a length of 15.0 in. to a length of 18.0 in.
EXAMPLE 1 Work done stretching spring
A spring of natural length 12 in. requires a force of 6.0 lb to stretch it 2.0 in. See Fig. 26.64. Find the work done in stretching it 6.0 in. From Hooke's law, we find the constant for the spring, and therefore f(x) as
Since the spring is to be stretched 6.0 in.a = 0, (it starts unstretched) and b = 6.0 (it is 6.0 in. longer than
Its normal length). Therefore, the work done in stretching it is
Problems involving work by a variable force arise in many fields of technology. On the following page is an illustration from electricity that deals with the motion of an electric charge through an electric field created by another electric charge.
