Give some example when tha work is +ve &-ve?

Dear student

Work is defined as scalar product between Force and displacement.

, here F is the force applied & S is the displacement

W = FS cos ,where is the angle between the vectors F and S.

cos can take positive or negative values depending on the values of .

For example: When in case of body sliding along a rough surface, force of friction acts opposite to the displacement. In such a case is 180⁰ & corresponding work done by friction on the body in motion is negative.

 

For a spring being stretched, a restoring force or spring force acts in the direction opposite to the stretch. Work done by the restoring force is always negative.

 

Positive work:

Ball in free fall, udner the effect of gravity. Here the force of gravity acts on the ball in the direction of fall of the ball. Hence the work done by gravity on freely falling ball is positive.

 

We hope that clarifies your doubt.

Regards

Team

TopperLearning