PSAT Math Multiple-Choice Question 131: Answer and Explanation

Question: 131

As an object moves through a fluid, the object experiences a force known as drag. For a given projected object area in meters squared and fluid density in kilograms per meter cubed, drag can be modeled by the equation , where R is drag force in Newtons, C is the coefficient of drag, and v is velocity in meters per second. Which of the following is equivalent to two Newtons? (Assume the object is moving at a constant speed.)

• A. The drag on an object with a coefficient of drag of 1 and a velocity of 2 meters per second
• B. The drag on an object with a coefficient of drag of 2 and a velocity of 1 meter per second
• C. The drag on an object with a coefficient of drag of 2 and a velocity of 2 meters per second
• D. The drag on an object with a coefficient of drag of 4 and a velocity of 0.25 meter per hour

Correct Answer: A

Explanation:

A

The question asks for the answer that is equivalent to two Newtons. Look through the question to find a mention of Newtons. In the equation, R is drag force in Newtons, so the correct answer will make R = 2. The other variables are C as the coefficient of drag and v as velocity in meters per second. Plug the values for C and v in the answer choices into the equation to determine which gives 2 for R. Start with (A). If the coefficient of drag is 1 and velocity in meters per second is 2, then C = 1 and v = 2. Plug those values into the equation to get R = , which becomes R = or R = 2. This matches the value given in the question, so stop here. The correct answer is (A).