A cup is sliding down an inclined surface that is not smooth. What is the correct free body diagram for the body?

Let's see the forces in the cup:

The gravitational force will act in the plane parallel to the inclined surface.

Because the surface is not smooth, we will have a friction force, which direction is opposite to the velocity vector.

The component of the gravitational force perpendicular to the surface is canceled with the normal force, so we will not have that in our diagram.

The correct option is not shown, so i will draw a simple sketch so you can identify the correct option:

Where the direction of the velocity is shown so we can know the direction of the friction force,

And we assume that both forces are applied on the center of mass, this is an oversimplified case, but this is the approach we usually take in this type of problems.

see earlier

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