What do you understand by positive work, negative work and zero work? Give at least two examples of each type.

Explanation

Since `W = vecF. vecS = FS cos theta`
i) Positive Work
When `theta` lies between `0^@ and 90^@, cos theta` is positive. Therefore, work done is positive.
`W = FS`
Example : Work done by the gravity on a freely falling body.
ii) Negative Work
When `theta` lies between `90^@ and 270^@, costheta` is negative. Therefore, work done is negative. i.e.,
`W =-FS `
Example: Work done against friction.
iii) Zero Work
When `theta = 90^@` or `270^@, cos theta` is zero i.e. `W = FS cos 90^@ = FS cos 270^@ = 0`
Example : A person holding a suitcase in his hand moves on a horizontal road, work done is zero.