Question

Newton`s second law of motion with free body diagram (FBD)

1. A 300g eraser rests on a table what is its normal force?

2. The eraser in #1 is placed in a table inclined @ 40°. What is its new normal force? Assume that the eraser is not sliding.

3. If the eraser in #2 begins sliding, what force parallel to the eraser is needed to prevent it from moving?

Answer 1

1.

$$N=mg=0.3(9.8)=2.94\ N$$

2.

$$N=mg\cos{40}=0.3(9.8)\cos{40}=2.25\ N$$

3.

$$F=mg\sin{40}=0.3(9.8)\sin{40}=1.89\ N$$