AP Physics C Mechanics Quiz: Newtons First Law

What this quiz covers

This quiz focuses on Newtons First Law, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Physics C Mechanics.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. The ball accelerates forward with the wagon due to inertia.
2. The ball remains at rest with respect to the ground. (correct answer)
3. The ball moves backward with a constant velocity relative to the ground.
4. The ball accelerates backward with respect to the ground.

Question 2

1. continuously fire its engines with a small, constant force to counteract cosmic drag.
2. periodically fire its engines to provide boosts that compensate for a natural tendency to slow down.
3. do nothing, as no net force is required to maintain a constant velocity. (correct answer)
4. fire its engines in the direction opposite to its velocity to prevent it from speeding up on its own.

Question 3

1. It continues because inertia maintains constant velocity when no net external force acts. (correct answer)
2. It continues because constant velocity requires a constant forward net force at all times.
3. It continues because its acceleration is zero only when mass is zero.
4. It continues because the road exerts a forward normal force that sustains motion.

Question 4

1. Its inertia maintains constant velocity when the net external force is approximately zero. (correct answer)
2. Its inertia actively produces forward motion, so no forces are ever needed.
3. A constant forward force from the ice must continuously act to maintain motion.
4. The puck accelerates because any moving object must experience a net external force.

Question 5

1. $mg$ (correct answer)
2. $\mu_k F$
3. $\mu_k mg$
4. $F$

Question 6

1. Greater than $Mg$
2. Less than $Mg$
3. Equal to $Mg$ (correct answer)
4. Zero

Question 7

1. The forces of tension and gravity on the toy are balanced by a third, unseen force.
2. The car's frame is non-inertial, and Newton's First Law only applies in inertial frames. (correct answer)
3. The tension in the string is exactly equal to the force of gravity, leading to a static situation.
4. The law is not violated because the toy's velocity relative to the car is indeed constant (zero).

Question 8

1. The static friction force must have the magnitude $f_s = \mu_s mg \cos\theta$.
2. The static friction force must be greater than the component of gravity along the incline.
3. The static friction force must be equal in magnitude to the component of gravity along the incline. (correct answer)
4. The static friction force must be zero because the block is not in motion.

Question 9

1. gravity acts on the ball equally in both reference frames.
2. the ground is the only true inertial frame, and the train's motion is relative to it.
3. both frames are moving with zero acceleration. (correct answer)
4. the laws of motion are simplest when viewed from these frames.

Question 10

1. $(-3\hat{i} + 4\hat{j}) \text{ N}$ (correct answer)
2. $(3\hat{i} - 6\hat{j}) \text{ N}$
3. $(0\hat{i} + 0\hat{j}) \text{ N}$
4. $(-3\hat{i} + 2\hat{j}) \text{ N}$

Question 11

1. $F_g > F_d$
2. $F_g < F_d$
3. $F_g = F_d$ (correct answer)
4. The relationship cannot be determined without knowing the parachutist's mass.

Question 12

1. A forward force from the initial push of the bowstring and the downward force of gravity.
2. Only the downward force of gravity. (correct answer)
3. A forward force to maintain its motion and the downward force of gravity.
4. There are no forces acting on the arrow because it is no longer being pushed.

Question 13

1. $20 \text{ N}$
2. $20 \cos(30^\circ) \text{ N}$ (correct answer)
3. $20 \sin(30^\circ) \text{ N}$
4. $0 \text{ N}$

Question 14

1. The object continues moving right but its speed increases.
2. The object's path curves, and it begins to move upwards and to the right.
3. The object instantaneously stops and remains at rest. (correct answer)
4. The object continues moving right but its speed decreases.

Question 15

1. A force with a magnitude equal to the puck's weight, acting perpendicular to the ice.
2. A constant horizontal force in the direction of the puck's velocity to maintain the speed.
3. A horizontal force that is directly proportional to the puck's speed.
4. Zero. (correct answer)

Question 16

1. The gravitational force is the only force acting on the crate, but it is not strong enough to cause motion.
2. The gravitational force and the normal force are the only forces, and they happen to be equal and opposite.
3. The vector sum of all forces acting on the crate is zero, maintaining its state of rest. (correct answer)
4. A static friction force is the primary force preventing the crate from starting to move on its own.

Question 17

1. The wrench appears to slow down and eventually reverse direction because the astronaut's reference frame changed velocity relative to the original inertial frame
2. The wrench continues at the same apparent velocity as before because Newton's first law applies equally in all inertial reference frames
3. The wrench appears to accelerate away from the astronaut because the astronaut is now in an accelerating reference frame due to the jetpack
4. The wrench appears to move faster in the same direction because the astronaut's motion created a relative velocity increase between them (correct answer)

Question 18

1. The student is correct because the system was initially at rest and tends to remain at rest according to Newton's first law
2. The student is correct because the forces on both blocks balance: tension equals weight for the hanging block and normal force balances weight for the table block
3. The student is incorrect because the hanging block experiences unbalanced gravitational force, creating net force on the system (correct answer)
4. The student is incorrect because Newton's first law only applies to individual objects, not to systems of connected objects

Question 19

1. The passenger is incorrect; the car's reference frame is non-inertial, so Newton's first law doesn't apply without including fictitious forces (correct answer)
2. The passenger is correct; this situation demonstrates that Newton's laws break down in accelerating vehicles due to relativistic effects
3. The passenger is correct; the coin's backward acceleration proves that objects naturally resist changes in their environment
4. The passenger is incorrect; friction from the dashboard actually pushes the coin backward, providing the necessary force for acceleration

Question 20

1. The physicist is correct because circular motion requires continuous centripetal acceleration, which necessitates net force and violates Newton's first law (correct answer)
2. The engineer is correct because the satellite maintains constant kinetic energy, which is the true measure of uniform motion in Newton's first law
3. The engineer is correct because in the absence of friction and air resistance, orbital motion represents the purest example of Newton's first law
4. The physicist is correct because satellites must continuously fire thrusters to maintain orbit, proving that external forces are required