Physics: Work Power & Energy

Formulas and other important things

Work done formula

W = F.s, where F is force and s is displacement.

The two can be written in i cap, j cap and k cap format.

These can also be integrated for force changing over time.

Positive or Negative work done

If the angle between the vectors is acute, then the work done is positive, and if it's obtuse, then it is negative.

Important things to remember about work

1. Work is defined for an interval or displacement, there isn't a term like instantaneous work like there is instantaneous velocity.

2. For a particular displacement, work done by a force is independent of type of motion, i.e., whether it moves with constant velocity, constant acceleration or retardation, etc.

3. For a particular displacement, work is independent of time. Work will be the same for same displacement whether the time taken is small or large.

4. When several forces act, work down by a force for a particular displacement is independent of other forces.

5. A force doesn't depend on the frame of reference but displacement does, which is why work is frame dependent and can be different in different frames of references.

6. The effect of work is either change in KE or PE.

Perpendicular force in work

When force is perpendicular to the displacement of a particle, the work done by that force is zero