A mass m is placed on a rough incline at an angle $\theta$ to the horizon. A force F is applied up the incline, to prevent the mass from sliding down the incline, and it is just enough to prevent the mass from sliding down the incline. Using the compass rose, the direction of the frictional force is along
A) a.
B) b.
C) c.
D) d.
E) e.

Question

A mass m is placed on a rough incline at an angle $\theta$ to the horizon. A force F is applied up the incline, to prevent the mass from sliding down the incline, and it is just enough to prevent the mass from sliding down the incline. Using the compass rose, the direction of the frictional force is along 
A) a. 
B) b. 
C) c. 
D) d. 
E) e.

Quizplus · Accepted Answer

The frictional force always acts opposite to the direction of motion or the impending motion. Here, the force F is preventing the mass from sliding down the incline and hence the frictional force will act opposite to the direction of F, which is along the incline in the downward direction. Therefore, the direction of the frictional force is along b.

A Mass M Is Placed on a Rough Incline at an Angle