AP Physics C: Mechanics Practice Quiz: Resistive Forces
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Test your understanding with short quizzes. This quiz has 10 questions to check your progress.
Question 1 of 10
All Questions (10)
A) It is a constant force that opposes gravity.
B) It is a force that depends on the object's position.
C) It is a velocity-dependent force acting in the opposite direction of velocity.
D) It is a force that only acts on objects at rest.
Correct Answer: C
The content explicitly defines a resistive force as 'a velocity-dependent force in the opposite direction of an object's velocity,' represented by the equation $\vec{F}_{r}=-k\vec{v}$.
A) The object's speed will increase at a constant rate.
B) The object's speed will remain constant.
C) The object's speed will decrease.
D) The object will immediately stop.
Correct Answer: C
A resistive force is always in the opposite direction of an object's velocity. According to Newton's second law, a net force opposite to the direction of motion will cause a deceleration, meaning the object's speed will decrease.
A) Equal to the resistive force.
B) Equal to the constant downward force (e.g., gravity).
C) Zero.
D) A constant, non-zero downward value.
Correct Answer: C
Terminal velocity is defined as the maximum, and therefore constant, speed. If the velocity is constant, the acceleration is zero. According to Newton's second law (F=ma), if the acceleration is zero, the net force on the object must also be zero.
A) Because the mass of the object is changing.
B) Because the resistive force is constant, but acceleration is not.
C) Because the force is a function of velocity, and acceleration is the time derivative of velocity.
D) Because the motion can only be described by algebraic equations.
Correct Answer: C
Newton's second law is $\sum \vec{F} = m\vec{a}$. The resistive force is a function of velocity ($\vec{F}_{r}=-k\vec{v}$), and acceleration is the derivative of velocity ($\vec{a} = d\vec{v}/dt$). Combining these results in an equation relating velocity to its own derivative, which is the definition of a differential equation.
A) The magnitude of the force is always negative.
B) The force vector is in the opposite direction of the velocity vector.
C) The force only applies when the velocity is decreasing.
D) The constant 'k' must be a negative number.
Correct Answer: B
In vector notation, a negative sign indicates that one vector points in the exact opposite direction of another. Thus, the negative sign signifies that the resistive force $\vec{F}_{r}$ is always directed opposite to the object's velocity $\vec{v}$.
A) It is equal to the force of gravity.
B) It is at its maximum possible value.
C) It is zero.
D) It is a small, non-zero constant.
Correct Answer: C
The resistive force is given by the equation $\vec{F}_{r}=-k\vec{v}$. If the object is dropped from rest, its initial velocity is zero. Substituting v=0 into the equation gives a resistive force of zero at that instant.
A) The object must be moving in a vacuum.
B) The only force on the object must be the resistive force.
C) A constant force and a resistive force must act in opposite directions.
D) The object's mass must be negligible.
Correct Answer: C
The content defines terminal velocity as the maximum speed achieved by an object 'moving under the influence of a constant force and a resistive force that are exerted on the object in opposite directions.' This balance of opposing forces is required.
A) Equal to g, the acceleration due to gravity.
B) A value greater than zero but less than g.
C) Zero.
D) Constantly changing.
Correct Answer: C
Terminal velocity is the 'maximum speed', which implies it is a constant speed. Acceleration is the rate of change of velocity. If velocity is constant, its rate of change is zero, meaning the acceleration is zero.
A) The net force increases, and the resistive force increases.
B) The net force decreases, and the resistive force increases.
C) The net force remains constant, and the resistive force increases.
D) The net force decreases, and the resistive force decreases.
Correct Answer: B
As the object falls, its speed increases. Since the resistive force is proportional to velocity ($\vec{F}_{r}=-k\vec{v}$), the resistive force increases. The net force is the difference between the constant downward force (gravity) and the increasing upward resistive force. Therefore, as the resistive force increases, the net force decreases, eventually becoming zero at terminal velocity.
A) Always zero.
B) Constant and non-zero.
C) Not constant.
D) Infinite.
Correct Answer: C
The resistive force depends on velocity. As velocity changes, the resistive force changes, which in turn changes the net force. According to Newton's second law, a changing net force results in a changing, non-constant acceleration (unless the net force is zero, as in the specific case of terminal velocity).