Day 21 MCAT Practice Question

Correct answer: B. First, we have to identify the forces acting on

the block. A gravitational force (mg) is acting downward, normal force (N) is

perpendicular to the incline, and the force F is parallel to the incline. It is important

to determine which component of gravitational force is acting parallel to the incline

to calculate the net force on this incline. In this case, that is (mg x sin(θ)).

Newton’s Second Law is useful to gain a better understanding of how these forces

combine to cause an upward acceleration of 2 m/s2 up the incline:

F - (mg (sinθ)) = ma

Where m = 2 2kg, g = 9.8 m/s2, θ is 30°, and a = 2 m/s2. The term on the right side

of the equation (ma) is simply equal to the force that contributes to the observed

acceleration (F = ma).

The component of the gravitational force that we are interested in is:

2 kg x 9.8 m/s2 x sin(30°) = 2 x 9.8 x 0.5 = 9.8 N

ma = 2 kg x 2 m/s2 = 4 N ← The mass of the block multiplied by the actual

acceleration due to the applied force

Therefore:

F - 9.8 = 4

F = 13.8N

Therefore, answer choice B is correct because it is closest to 13.8 N.