## Work, energy and power

It was shown in chapter 18 that force = mass × acceleration, and that if an object is dropped from a height it has a constant acceleration of around 9.81 m/s2. Thus if a mass of 8 kg is lifted vertically 4 m, the work done is given by:

work done = force × distance = (mass × acceleration) × distance = (8 × 9.81) × 4 = 313.92 J

The work done by a variable force may be found by determining the area enclosed by the force/distance graph using an approximate method such as the midordinate rule. To determine the area ABCD of Figure 20.3 using the mid-ordinate rule:

(i) Divide base AD into any number of equal intervals, each of width d (the greater the number of intervals, the greater the precision).