AP Physics C: Mechanics Practice Quiz: Newton's Second Law
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Test your understanding with short quizzes. This quiz has 9 questions to check your progress.
Question 1 of 9
All Questions (9)
A) The mass of the system
B) The magnitude of the net force exerted on the system
C) The velocity of the system's center of mass
D) The time over which a force is applied
Correct Answer: B
Newton's second law, represented by the equation $\vec{a}_{sys}=\frac{\sum\vec{F}}{m_{sys}}$, states that acceleration ($a_{sys}$) is proportional to the net force ($\sum\vec{F}$).
A) West
B) North
C) East
D) The direction cannot be determined without knowing the system's initial velocity.
Correct Answer: C
The provided content specifies that the acceleration of a system's center of mass is 'in the same direction as that net force.' Therefore, if the net force is to the east, the acceleration must also be to the east.
A) When a single, constant external force is applied.
B) When the net external force exerted on the system is zero.
C) When the system's mass is very large.
D) When the system is accelerating.
Correct Answer: B
The content states that the velocity of a system's center of mass will only change if a nonzero net external force is exerted on it. Therefore, for the velocity to remain constant (not change), the net external force must be zero.
A) It is halved.
B) It remains the same.
C) It is doubled.
D) It is quadrupled.
Correct Answer: C
Based on the equation $\vec{a}_{sys}=\frac{\sum\vec{F}}{m_{sys}}$, acceleration is directly proportional to the net force. If the net force ($\sum\vec{F}$) is doubled and mass ($m_{sys}$) is constant, the acceleration ($a_{sys}$) must also double.
A) The acceleration will be quadrupled.
B) The acceleration will be doubled.
C) The acceleration will remain the same.
D) The acceleration will be halved.
Correct Answer: D
The equation $\vec{a}_{sys}=\frac{\sum\vec{F}}{m_{sys}}$ shows that acceleration is inversely proportional to mass. If the mass ($m_{sys}$) is doubled while the net force ($\sum\vec{F}$) is held constant, the acceleration will be reduced to one-half of its original value.
A) The system must have zero mass.
B) The forces acting on the system must be internal.
C) A nonzero net external force must be exerted on the system.
D) The system must be in a vacuum.
Correct Answer: C
The provided text explicitly states: 'The velocity of a system's center of mass will only change if a nonzero net external force is exerted on that system.'
A) The gravitational force on the system
B) The largest individual force on the system
C) The net force exerted on the system
D) The force exerted by the system on its surroundings
Correct Answer: C
The symbol $\sum$ denotes a summation. In this context, $\sum\vec{F}$ represents the vector sum of all forces exerted on the system, which is defined as the net force.
A) The object is gaining speed.
B) There is only one force acting on the object.
C) The net external force on the object is not zero.
D) The object's mass is changing.
Correct Answer: C
Acceleration is a change in velocity. The content states that a system's velocity only changes if a nonzero net external force is exerted on it. Therefore, if an object is accelerating, there must be a nonzero net external force acting on it.
A) Acceleration is proportional to the net force and in the same direction.
B) Acceleration is inversely proportional to the net force and in the opposite direction.
C) Acceleration is independent of the net force.
D) Acceleration is proportional to the net force but always in the opposite direction.
Correct Answer: A
The provided content explicitly states that the acceleration of a system's center of mass has a magnitude 'proportional to the magnitude of the net force exerted on the system and is in the same direction as that net force.'