Question

A 2-kg wood block is pulled by a string across a rough horizontal floor. The string exerts a tension force of 30 n on the block at an angle of 20º above the horizontal. The block moves at constant speed. If the block is pulled for a distance of 3. 0 m, how much work is done by the tension force?.

Answer 1

Only the horizontal component (the component parallel to the floor) of tension does work on the block. This parallel component has magnitude

(30 N) cos(20°) ≈ 28.2 N

and acts over a distance of 3.0 m, so it performs

(28.2 N) (3.0 m) ≈ 85 J

of work