A bicyclist rides 2.90 km due east, while the resistive force from the air has a magnitude of 8.95 N and points due west. The rider then turns around and rides 2.90 km due west, back to her starting point. The resistive force from the air on the return trip has a magnitude of 8.95 N and points due east. Find the work done by the resistive force during the round trip.

A) - 16.8 Kj

Explanation:

We know that the work done W on an object by a constant force F is given by;

W = (Fcosθ)S

Where S is displacement or distance and θ is the angle between F and S.

A) For the first round trip, the displacement and the resistive force are in the west direction and so the angle between F and S is called θ1 which is equal to 180°.

S = 2.9km = 2900m

So, work done for this first trip is;

W1 = (2.9cos180) x 2900 = - 8.4 Kj

For the second round trip, the displacement and the resistive force are in the west direction and so the angle between F and S is called θ2 which is equal to 180°.

S = 2.9km = 2900m

So, work done for this second trip is;

W2 = (2.9cos180) x 2900 = - 8.4 Kj

Thus, Total work done by the resistive force through the round trip is;

W = W1 + W2 = - 8.4 - 8.4 = - 16.8 Kj

i think the answer is a, hope this : )