Question

Express the work in terms of l, f, and θ. remember to use radians, not degrees, for any angles that appear in your answer.

Answer 1

Assuming I see a force F acting on an object at an angle theta with the horizontal pushing it through a rough surface over a distance L such that the horizontal component is just required to overcome friction.

Then work done is
W=FLcos(theta)

(Read assumptions above due to lack of diagram)