Question

Name the force which always does negative work on a body. Why does it do only negative

work?​

Answer 1

Answer:

$frictional \: force$

frictional force only do negative work on a body as it always tends to stop the moving body or to reduce it's speed. in other words it opposes the motion is the body

Answer 2

Friction always does negative work on a body.

Let's see a detailed explanation:

• The work done by a force is negative, when the angle between the force vector and the displacement vector is obtuse ( i.e. > 90°).

Now, whenever an object moves on a rough surface, the frictional force vector is directed opposite to the displacement vector.

So, the angle between the two vectors is 180°.

Hence, the work done by frictional force is:

$W = force \times d \times \cos( \theta)$

$\implies \: W = f \times d \times \cos( {180}^{ \circ} )$

$\implies \: W = f \times d \times ( - 1)$

$\implies \: W = - fd$

Hence, friction always does negative work.