AP Physics 1 Quiz: Circular Motion

What this quiz covers

This quiz focuses on Circular Motion, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Physics 1.

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. Upward, because the mass is about to move downward
2. Downward, toward the center of the circle (correct answer)
3. Horizontally, in the direction of motion
4. Zero, because the speed is constant

Explanation: This question tests understanding of acceleration in vertical circular motion. At the top of a vertical circle where the mass moves horizontally, the acceleration must point toward the center of the circle, which is downward (B). This centripetal acceleration is responsible for changing the direction of the velocity vector from horizontal to downward as the mass continues its circular path. The acceleration is not upward (A) - that would cause the mass to slow down and reverse direction, and it cannot be horizontal (C) as that would not curve the path downward. Remember that in circular motion, acceleration always points toward the center regardless of whether the circle is horizontal or vertical.

Question 2

1. The skater's inertia pulling outward
2. The rope's tension pulling toward the post (correct answer)
3. A separate centripetal force in addition to tension
4. The skater's velocity pushing the skater inward

Explanation: This question assesses understanding of the source of centripetal force in uniform circular motion. Centripetal acceleration toward the center is provided by a net force in that direction, such as tension in this case. The tension in the rope pulls inward, serving as the centripetal force to keep the skater circling. No outward forces act; the motion is maintained by this inward net force. Choice A is a distractor attributing the force to inertia pulling outward, which confuses the tendency to move tangentially with an actual force. For identifying centripetal forces, examine real forces acting on the object and determine which provides the inward component.

Question 3

1. Tangent to the circle, in the direction of motion
2. Radially outward, away from the center
3. Toward the center of the circle (northward) (correct answer)
4. Zero, because the speed is constant

Explanation: This question assesses understanding of net force direction in horizontal uniform circular motion. The net force provides centripetal acceleration toward the center, maintaining the circular path. This force is inward, countering the tendency to move in a straight line. At the southmost point, the center is northward, so net force points north. Choice B is a distractor implying an outward force, which might confuse centripetal with centrifugal concepts. Always remember that in circular motion problems, the net force direction is toward the center, helping to identify it regardless of the setup.

Question 4

1. North, because the velocity is north
2. South, opposite the motion
3. West, away from the center
4. East, toward the center of the circle (correct answer)

Explanation: This question assesses understanding of acceleration direction in circular motion on a path. Centripetal acceleration points toward the center, perpendicular to the tangential velocity. The net force causing this is inward, maintaining the curve. At the westernmost point moving north, the center is eastward, so acceleration is east. Choice C is a distractor implying westward away from the center, possibly confusing with centrifugal ideas. To determine directions in such scenarios, sketch the position and velocity, then point acceleration inward toward the circle's center.

Question 5

1. Toward the west (toward the center of the circle) (correct answer)
2. Toward the east (away from the center)
3. Toward the north (tangent to the circle at that point)
4. Zero, because the velocity is not changing in magnitude

Explanation: This question tests understanding of net force direction in horizontal circular motion. When the stopper is at the easternmost point of its circular path, the net force must point toward the center of the circle, which is west (A). This centripetal force is what causes the continuous change in the velocity's direction, keeping the stopper moving in a circle rather than a straight line. The force cannot point away from the center (B) as this would cause the stopper to spiral outward, and it cannot be tangential (C) as this would change the speed rather than just the direction. The strategy is to always identify the center of the circular path and remember that net force points from the object toward that center.

Question 6

1. Directly outward from the center
2. Along the tangent to the circle at the release point (correct answer)
3. Directly toward the center
4. It remains at rest momentarily due to inertia

Explanation: This question tests understanding of motion after centripetal force removal. While the ball moves in a circle, the string provides centripetal force toward the center, continuously changing the ball's direction. When the string breaks, this inward force disappears, and by Newton's first law, the ball continues with the velocity it had at the instant of release. Since velocity in circular motion is always tangent to the circle, the ball moves along the tangent at the release point. Choice A incorrectly suggests outward motion, confusing the absence of inward force with the presence of an outward force. The strategy is to recognize that objects continue with their instantaneous velocity when forces are removed, and velocity in circular motion is always tangential.

Question 7

1. East, in the direction of motion
2. Toward the center of the circle (west) (correct answer)
3. Upward, because the string pulls up
4. Away from the center due to a centrifugal force

Explanation: This question assesses understanding of centripetal acceleration in uniform circular motion. In uniform circular motion, the centripetal acceleration always points toward the center of the circle, changing the direction of the velocity while keeping the speed constant. The net force, according to Newton's second law, must also point toward the center to provide this acceleration. For the ball at the east point, the center is to the west, so both acceleration and net force are westward. Choice D is incorrect because centrifugal force is a fictitious force in non-inertial frames and does not explain acceleration in the inertial frame. To analyze direction in circular motion, identify the center and remember acceleration is radial inward.

Question 8

1. Toward the center of the circle (south) (correct answer)
2. North, because the car is moving north there
3. Tangent to the track, in the direction of motion
4. Outward from the center because circular motion requires an outward force

Explanation: This question assesses understanding of net force in uniform circular motion. In uniform circular motion, the centripetal acceleration always points toward the center of the circle, changing the direction of the velocity while keeping the speed constant. The net force, according to Newton's second law, must also point toward the center to provide this acceleration. For the car at the northmost point, the center is to the south, so the net force points south. Choice D is incorrect because there is no outward force required; the inward net force causes the centripetal acceleration. To solve circular motion problems, always remember that the net force must provide the centripetal acceleration towards the center.

Question 9

1. It stays the same
2. It doubles
3. It quadruples (correct answer)
4. It becomes half as large

Explanation: This question tests understanding of how centripetal force depends on speed. The centripetal force formula is F = mv²/r, showing that force is proportional to the square of speed. When speed doubles, the required centripetal force increases by a factor of 2² = 4, or quadruples. This quadratic relationship means small speed increases require much larger force increases. Choice B incorrectly assumes a linear relationship between force and speed. To solve problems about changing circular motion parameters, use the centripetal force formula to identify which variables change and how they affect the required force.

Question 10

1. Tangent to the circle in the direction of motion
2. Radially inward, toward the center of the circle (correct answer)
3. Radially outward, away from the center due to a centrifugal force
4. Zero because the speed is constant

Explanation: This question tests understanding of acceleration direction in circular motion. When an object moves in a circle at constant speed, it continuously changes direction, requiring an acceleration toward the center of the circle. This centripetal acceleration points radially inward at every point on the path, including point P. The common misconception in choice D assumes that constant speed means zero acceleration, but acceleration includes changes in direction, not just speed. For any circular motion problem, remember that acceleration always points toward the center when speed is constant.

Question 11

1. Along the string, toward the student's hand (the center) (correct answer)
2. Along the direction of motion because speed is constant
3. Opposite the direction of motion to keep the speed constant
4. Radially outward due to centrifugal force from the motion

Explanation: This question addresses acceleration direction when tension provides the centripetal force. In horizontal circular motion at constant speed, the stopper requires centripetal acceleration directed toward the center (the student's hand). Since string tension is the only horizontal force, it must point along the string toward the center, causing acceleration in the same direction. The velocity is tangent to the circle, but acceleration points radially inward to change the velocity's direction. Choice D incorrectly references centrifugal force, which is not a real force in an inertial frame. For circular motion problems, identify which real force provides the centripetal acceleration—here it's the string tension pulling inward.

Question 12

1. Toward the center of the circle (southward) (correct answer)
2. Northward, because the car is moving north at that point
3. Outward (northward) due to a centrifugal force
4. Tangent to the path, in the direction of motion

Explanation: This question assesses understanding of net force in uniform circular motion. In uniform circular motion, the centripetal acceleration requires a net force directed toward the center of the circle. This net force provides the inward pull necessary to maintain the circular path at constant speed. For the car at the northmost point, the center is southward, so the net force points south. Choice C is a distractor that mentions an outward centrifugal force, which is not a real force but a perceived effect in non-inertial frames. To analyze net force in circular motion, remember it always points toward the center to provide centripetal acceleration, irrespective of the motion's direction.

Question 13

1. It accelerates outward because the centripetal force is gone
2. It has approximately zero acceleration and moves in a straight line tangent to the circle (correct answer)
3. It accelerates toward the center due to its previous motion
4. It accelerates in the direction opposite its velocity to slow down

Explanation: This question tests understanding of motion when centripetal force is removed. When the string breaks, the centripetal force disappears, so the puck has approximately zero acceleration and continues moving in a straight line tangent to the circle (B). This follows Newton's first law - without a net force, the puck maintains its velocity at the instant of release, which was tangent to the circle. The puck doesn't accelerate outward (A) because there's no force pushing it outward, and it doesn't accelerate toward the center (C) because the string tension that provided centripetal force is gone. The strategy is to apply Newton's first law: when forces become zero, objects maintain their instantaneous velocity.

Question 14

1. Upward, because the string pulls upward
2. Toward the center of the circle (leftward) (correct answer)
3. In the direction of motion (tangent to the circle)
4. Radially outward, away from the center

Explanation: This question assesses understanding of centripetal acceleration in uniform circular motion. In uniform circular motion, the centripetal acceleration is always directed toward the center of the circle, perpendicular to the velocity. This acceleration arises from a net force that points inward, changing the direction of the velocity while keeping the speed constant. For the rubber stopper at the rightmost point, the center is to the left, so the acceleration is leftward. A common distractor is choice D, which suggests a radially outward direction, but this confuses the fictitious centrifugal force with actual acceleration in the inertial frame. To determine the direction of acceleration in circular motion, always identify the center and point toward it, regardless of the object's position.

Question 15

1. An outward centrifugal force exerted by the puck
2. A tangential component of the tension force
3. The net inward force provided by the string tension (correct answer)
4. The puck's velocity, which points toward the center

Explanation: This question tests understanding of the cause of centripetal acceleration in circular motion. For the puck to move in a circle at constant speed, it needs a centripetal force directed toward the center. The string tension provides this inward force, which causes the centripetal acceleration according to Newton's second law. Since the table is frictionless and the motion is horizontal, the only horizontal force is the string tension pulling inward. Choice A incorrectly mentions "centrifugal force," which is not a real force but rather a fictitious force that appears only in rotating reference frames. The key insight is that centripetal acceleration is caused by whatever real forces act toward the center—in this case, the string tension.

Question 16

1. Downward, since gravity points downward
2. Upward, toward the center of the circle (correct answer)
3. Tangent to the path in the direction of motion
4. Radially outward, away from the center

Explanation: This question assesses understanding of centripetal acceleration in vertical circular motion. Even in a vertical circle, the centripetal acceleration points toward the center, required for the curved path. The net force causing this acceleration varies with position due to gravity, but the acceleration direction remains inward. At the bottom, the center is upward, so acceleration is upward. Choice D is a distractor implying an outward direction, which might stem from misunderstanding inertia or fictitious forces. When solving for acceleration direction in circular motion, consistently direct it toward the center, adjusting for any additional forces like gravity in calculations.

Question 17

1. Radially inward, toward the center of the circle (correct answer)
2. Tangentially, in the direction of the ball's velocity
3. Radially outward, away from the center due to a centrifugal force
4. Zero, because the speed is constant

Explanation: This question tests understanding of acceleration direction in circular motion. When an object moves in a circle at constant speed, it experiences centripetal acceleration that always points toward the center of the circle, making the answer radially inward (A). Even though the speed is constant, the velocity vector is constantly changing direction, requiring an acceleration perpendicular to the velocity. The ball's acceleration cannot be tangential (B) because that would change the speed, and there is no such thing as centrifugal force (C) in an inertial reference frame. A key strategy is to remember that circular motion always requires center-pointing acceleration to continuously change the direction of velocity.

Question 18

1. Toward the center of the circle
2. Straight outward from the center
3. Along the tangent to the circle at that point (correct answer)
4. It momentarily stops because the centripetal force is gone

Explanation: This question assesses understanding of motion after loss of centripetal force in circular motion. In uniform circular motion, the centripetal acceleration always points toward the center of the circle, changing the direction of the velocity while keeping the speed constant. The net force, according to Newton's second law, must also point toward the center to provide this acceleration. When the string breaks, the net force vanishes, and by Newton's first law, the stopper moves tangent to the circle. Choice B is incorrect because there is no outward force; the motion becomes linear tangent to the path. To predict motion after force removal, apply the principle of inertia and continue with the instantaneous velocity vector.

Question 19

1. A tangential force from its forward motion causes the acceleration
2. An outward centrifugal force balances gravity
3. Earth's gravitational force provides the inward net force (correct answer)
4. No net force is needed because the speed is constant

Explanation: This question assesses understanding of forces causing centripetal acceleration in uniform circular motion. In uniform circular motion, the centripetal acceleration always points toward the center of the circle, changing the direction of the velocity while keeping the speed constant. The net force, according to Newton's second law, must also point toward the center to provide this acceleration. For the satellite, Earth's gravity provides this inward net force. Choice B is incorrect because centrifugal force is fictitious and does not balance gravity; gravity is the centripetal force. To identify forces in circular motion, consider only real forces that provide the inward net force for acceleration.

Question 20

1. It is zero because the speed is constant
2. It points toward the center because the net force is inward (correct answer)
3. It points tangent to the circle because motion is circular
4. It points outward because centrifugal force dominates

Explanation: This question assesses understanding of acceleration in uniform circular motion. In uniform circular motion, the centripetal acceleration always points toward the center of the circle, changing the direction of the velocity while keeping the speed constant. The net force, according to Newton's second law, must also point toward the center to provide this acceleration. With tension toward the center, the acceleration points inward toward the center. Choice D is incorrect because there is no outward centrifugal force; acceleration follows the net force inward. To relate force and acceleration in circular motion, apply F_net = ma_c, where a_c is v²/r toward the center.