MCAT Physics Question — Object Acceleration
 by
 Oct 08, 2017
 Reviewed By: Liz Flagge
An object rests on a plane, with an angle of incline, θ, an acceleration due to gravity, g, and a coefficient of friction μ between the object and the plane. Which of the following gives the acceleration of the object?
A. a = g sin θ
B. a = g (sin θ – cos θ)
C. a = g (cos θ – μ sin θ)
D. a = g (sin θ – μ cos θ)
Click for Explanation
The force of gravity down the plane is given by F_{g} = mg sin θ. The frictional force is given by F_{f} = μ mg cos θ.
Thus, we can set up the overall equation:
F_{net} = F_{g} – F_{f}
Applying Newton’s Second Law, we can rewrite the equation as:
ma = F_{g} – F_{f}
Substituting the equations given for F_{f} and F_{g} we get:
ma = mg sin θ – μ mg cos θ
Canceling out “m” throughout the equation and factoring out the “g” leaves us with:
a = g (sin θ – μ cos θ)
Thus, choice (D) is the right answer.
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