TOLC-med 2007 resultant forces

Practice Question Solving
1

A body is subjected to a force of module F constant and parallel to the support plane; it is verified that the resulting motion is rectilinear and uniform with speed V.
From this we conclude that the friction force:

A) is orthogonal to the plane of motion
B) is equal and opposite to the force F
C) is = 0
D) is half the force F and has the same direction and sense
E) is half the force F and has the same direction and opposite sense

i thought it should be E) but the answer is B). How can the body move if the friction is equal and opposite??

2

Hi, I understood this question as “Force F is not directly exerted to the object (just support the object), and the object moves in straight line and uniform."

I think it means that there is no direct net external force in this case, and to keep the whole thing in uniform, the friction should be there in same quantity / opposite direction.

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