Does Static Friction Contribute to Work in an Inclined Car?

[Zhalfirin88]

Homework Statement

A car is going down an incline with a constant acceleration.
How much work was done on the car by the force of the road going down the hill? (neglect energy losses due to air resistance, rolling friction, etc.)

The Attempt at a Solution

There are 2 forces acting on the car from the road, the normal force and static friction. But the displacement of both the normal force and static friction are both 0, so how is static friction doing work?

 

[Doc Al]

There are 2 forces acting on the car from the road, the normal force and static friction. But the displacement of both the normal force and static friction are both 0, so how is static friction doing work?

Technically, the static friction does no work on the car.

 

[Zhalfirin88]

That's exactly what I put, 0, and it was marked wrong. I'm trying to figure out why it was marked wrong

 

[azizlwl]

Work done, ΔW= F.Δx
Because F_f opposes the motion, it is directed opposite to x

the work done on the car by friction,
W=-F_f.x

 

[Doc Al]

That's exactly what I put, 0, and it was marked wrong. I'm trying to figure out why it was marked wrong

They probably wanted you to calculate F*Δx, where Δx is the displacement of the center of mass, not the point of contact. Strictly speaking, that's not work, but pseudowork.