The figure (Fig.1) shows a block of mass *M*, placed on a plane surface AB inclined at an angle *θ *with the horizontal AC. Answer the questions relevant to the situations given below:

**(a)** Initially the frictional force *F _{f} *between the inclined plane and the block is sufficient to keep the block at rest. The coefficient of static friction between the incline and the block is

*μ*. On the dot below (Fig.3)that represents the block, draw and label a free body diagram for the block in this situation.

**(b)** Determine the magnitude of the frictional force on the block in the situation described in part (a).

**(c)** A force* F* is now applied on the block in a direction making an angle α (Fig.2) with the inclined plane so that the block just moves up the plane.

Determine the magnitude of the *minimum* force (*F*_{min}) required for pulling the block up the plane.

(d) The inclination of the plane AB with the horizontal is made equal to 30º. When a block of mass 2 kg is placed on the incline and a gentle push is given, the block moves down the plane with constant velocity of 0.2 ms^{–1}.

Determine the magnitude of the frictional force on the block and the coefficient of friction in this situation, assuming that g = 10 ms^{–2}.

Even though this question is meant for AP Physics B students, AP Physics C aspirants also may work it out. The question can be easily modified to suit to the AP Physics C students.

Try to answer the above question which carries 15 points. You can take about 17 minutes for answering it. I’ll be back shortly with a model answer for you.

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