- A 0.15 kg ball strikes a stationary 2.0 kg bowling pin and rebounds. During the brief contact, the ball and pin exert forces on each other. How does the magnitude of the force on the pin by the ball compare to the magnitude of the force on the ball by the pin?
Answer: The forces are equal in magnitude and opposite in direction.
This problem involves Newton's third law during a collision between a ball and bowling pin. During contact, the ball exerts a force on the pin, and the pin exerts an equal and opposite force on the ball. These forces form an action-reaction pair that must be equal in magnitude throughout the collision, regardless of the objects' masses or how they move afterward. The forces act on different objects—the ball's force acts on the pin, while the pin's force acts on the ball. Choice D incorrectly suggests that the pin's greater mass affects the force equality, but Newton's third law ensures the forces are always equal. When analyzing collisions, focus on the forces during contact and remember that action-reaction pairs are equal regardless of mass differences or motion changes.
- A magnet attracts a steel paperclip while both are held at rest a few centimeters apart by separate supports. Comparing the magnetic force on the paperclip and the magnetic force on the magnet, which is correct?
Answer: The forces are equal in magnitude and opposite in direction.
This question tests understanding of Newton's third law for non-contact forces. The magnet exerts an attractive magnetic force on the paperclip, and simultaneously the paperclip exerts an equal magnitude attractive force back on the magnet. These interaction forces are always equal in magnitude and opposite in direction, even though they act at a distance without physical contact. The forces act on different objects: the magnet's force acts on the paperclip, while the paperclip's force acts on the magnet. Choice A incorrectly assumes the magnet exerts a larger force because it's the "source" of magnetism, but Newton's third law applies equally to all interactions. Remember that Newton's third law applies to all forces, whether contact or non-contact.
- A 2.0 kg book rests on a table. The book and table exert contact forces on each other at the surface. How does the force exerted by the table on the book compare to the force exerted by the book on the table?
Answer: The forces are equal in magnitude and opposite in direction.
This question involves Newton's third law for a book resting on a table. At the contact surface, the table exerts an upward normal force on the book, and the book exerts an equal downward force on the table. These forces are equal in magnitude and opposite in direction, forming an action-reaction pair that acts on different objects. The fact that gravity pulls on the book is separate from this contact interaction—the book-table forces are equal regardless of other forces acting on either object. Choice B incorrectly conflates the gravitational force on the book with the contact force between book and table. To apply Newton's third law correctly, focus on forces at the specific interaction point and ignore other forces acting elsewhere on the objects.
- A 0.20 kg cart on a level track is pulled rightward by a student using a string attached to a force sensor. The sensor reads 3.0 N while the cart moves at constant speed. Comparing the interaction forces between the student (via the string) and the cart, which statement is correct?
Answer: The student pulls on the cart with 3.0 N, and the cart pulls on the student with 3.0 N in the opposite direction.
This question tests understanding of Newton's third law. When the student pulls on the cart with 3.0 N through the string, the cart simultaneously pulls back on the student with 3.0 N in the opposite direction. These interaction forces are always equal in magnitude and opposite in direction, regardless of the masses of the objects or their motion. The forces act on different objects: the student's force acts on the cart, while the cart's force acts on the student. Choice A incorrectly suggests that mass differences affect the interaction forces, when Newton's third law applies equally regardless of mass. To solve Newton's third law problems, identify the two interacting objects and remember that they always exert equal and opposite forces on each other.
- A magnet is held near a steel paper clip, and the paper clip is attracted toward the magnet. Consider the interaction between the magnet and the paper clip. Which statement correctly compares the forces they exert on each other?
Answer: The magnet and paper clip exert forces on each other equal in magnitude and opposite in direction.
This problem explores Newton's third law in non-contact forces like magnetism. The third law applies to all interactions, stating forces are equal in magnitude and opposite in direction. The magnet exerts a magnetic force on the paper clip equal and opposite to the force the paper clip exerts on the magnet. These forces act on different objects and are equal regardless of which moves or attracts. Distractor A mistakenly ties force inequality to observed motion, but motion results from net forces, not the pair. Broadly, extend third law to all force types by identifying pairs and confirming equality before considering causes of motion.
- A 0.20 kg hockey puck slides across ice and collides head-on with a 1.0 kg stationary puck. During the brief collision, both pucks are in contact and exert forces on each other. How do the force magnitudes compare during the contact?
Answer: The forces are equal in magnitude and opposite in direction at each instant of contact.
This question tests knowledge of Newton's third law in the context of collisions. Newton's third law states that for every action force, there is an equal and opposite reaction force between interacting objects. During the collision, the force the 0.20 kg puck exerts on the 1.0 kg puck is equal in magnitude and opposite in direction to the force the 1.0 kg puck exerts on the 0.20 kg puck. These forces act on different objects and are independent of their masses or velocities, focusing solely on the interaction. Choice A is a distractor that wrongly prioritizes mass over the equality of interaction forces, but mass affects acceleration, not the force pair itself. A useful strategy is to isolate the interaction pair and apply Newton's third law directly, then use Newton's second law to find accelerations if needed.
- A 0.30 kg ball hangs from a string and is pulled sideways by a student's hand, holding it at rest at an angle. The hand remains in contact with the ball. Compare the force of the hand on the ball to the force of the ball on the hand.
Answer: They are equal in magnitude and opposite in direction.
This question assesses understanding of Newton's third law of motion. Newton's third law states that for every action force, there is an equal and opposite reaction force. The force of the hand on the ball and the force of the ball on the hand are an action-reaction pair. These forces are equal in magnitude but opposite in direction, and they act on different objects—the hand and the ball. A common distractor is choice A, which wrongly suggests the hand's force is greater because the ball is not moving, but third-law pairs remain equal even when the system is in equilibrium. To apply Newton's third law effectively, identify the interacting objects and remember that their mutual forces are always equal and opposite, independent of other system details.
- A 0.20 kg ball moving right strikes a stationary 5.0 kg bowling pin and rebounds left. During contact, how do the forces compare?
Answer: The forces are equal in magnitude and opposite in direction.
This question tests Newton's third law of motion. During the collision between the ball and pin, they exert forces on each other that form an interaction pair. According to Newton's third law, these interaction forces are always equal in magnitude and opposite in direction—the ball pushes on the pin while the pin simultaneously pushes back on the ball with equal force. These forces act on different objects and exist only during the contact time. Choice A incorrectly relates mass to force magnitude, but Newton's third law forces are always equal regardless of mass differences (what differs is the acceleration each object experiences). The key strategy is to remember that in any collision, the forces between colliding objects are always equal and opposite, independent of their masses or velocities.
- A 0.15 kg baseball moving horizontally strikes a 0.90 kg bat that is held stationary, and they remain in contact briefly. During contact, compare the force of the bat on the ball to the force of the ball on the bat.
Answer: They are equal in magnitude and opposite in direction.
This question assesses understanding of Newton's third law of motion. Newton's third law states that for every action force, there is an equal and opposite reaction force. In this case, the force of the bat on the ball and the force of the ball on the bat form an action-reaction pair. These forces are equal in magnitude but opposite in direction, and they act on different objects—the bat and the ball. A common distractor is choice A, which incorrectly asserts that the bat's force is greater due to its mass, but third-law pairs are equal irrespective of mass differences. To apply Newton's third law effectively, identify the interacting objects and remember that their mutual forces are always equal and opposite, independent of other system details.
- A 2.0 kg block is pulled to the right by a horizontal rope with tension T, sliding across a rough surface. While the rope remains taut, compare the force of the rope on the block to the force of the block on the rope.
Answer: They are equal in magnitude and opposite in direction.
This question assesses understanding of Newton's third law of motion. Newton's third law states that for every action force, there is an equal and opposite reaction force. The force of the rope on the block and the force of the block on the rope are an action-reaction pair. These forces are equal in magnitude but opposite in direction, and they act on different objects—the rope and the block. A common distractor is choice B, which mistakenly suggests the rope's force is greater due to friction on the block, but external factors like friction do not affect the equality of third-law pairs. To apply Newton's third law effectively, identify the interacting objects and remember that their mutual forces are always equal and opposite, independent of other system details.
- A person stands on a bathroom scale in an elevator. The person's feet push down on the scale, and the scale pushes up on the person. At a given instant (regardless of whether the elevator is speeding up or slowing down), how do these two forces compare in magnitude?
Answer: The forces are equal in magnitude and opposite in direction.
This question tests Newton's third law of motion. The person's feet and the scale form an interaction pair—the feet push down on the scale, and the scale pushes up on the feet with a force equal in magnitude and opposite in direction. These forces act on different objects (one on the scale, one on the person) and are always equal at any given instant. Whether the elevator is accelerating upward, downward, or moving at constant velocity doesn't change this fundamental relationship between the interaction forces. Choice A incorrectly confuses the magnitude of these interaction forces with the scale reading, which can vary with acceleration. Remember that Newton's third law applies to all interactions—the forces between two objects are always equal in magnitude.
- A 1200 kg car is being towed at constant speed by a truck using a taut rope on a level road. Focus on the interaction between the rope and the car (at the attachment point). Which statement correctly compares the forces?
Answer: The rope pulls on the car with the same magnitude force that the car pulls on the rope, in opposite directions.
This question examines Newton's third law in tension forces during towing. Per Newton's third law, the force one object exerts on another is matched by an equal and opposite force from the second object. The rope pulls on the car with the same magnitude as the car pulls back on the rope, but in the opposite direction. These forces are on different objects—the rope and the car—and remain equal even at constant speed. Choice B incorrectly links force magnitude to mass, but third-law pairs are independent of mass differences. To generalize, always pair forces between two objects and verify equality before considering overall system dynamics like acceleration.
- A satellite and Earth attract each other gravitationally while the satellite orbits. Consider the gravitational force Earth exerts on the satellite and the gravitational force the satellite exerts on Earth. Which statement best compares these two forces?
Answer: The forces are equal in magnitude and opposite in direction.
This question tests Newton's third law applied to gravitational forces between Earth and a satellite. Earth exerts a gravitational force on the satellite, and the satellite exerts an equal gravitational force back on Earth. These forces are equal in magnitude and opposite in direction, forming an action-reaction pair that acts on different objects. The vastly different masses of Earth and the satellite don't affect the equality of forces—Newton's third law applies to all interactions including gravity. Choice A incorrectly assumes that Earth's greater mass means it exerts a greater force, confusing force with acceleration (which would indeed be different). To solve problems involving Newton's third law, remember that interaction forces are always equal regardless of mass differences or resulting accelerations.
- A swimmer pushes backward on the pool wall during a turn. The wall pushes forward on the swimmer during the same contact. While the swimmer's feet are in contact with the wall, how do the magnitudes of these two forces compare?
Answer: They are equal in magnitude and opposite in direction.
This question tests Newton's third law of motion. During the turn, the swimmer's feet and the wall form an interaction pair—the feet push backward on the wall, and the wall pushes forward on the feet with a force equal in magnitude and opposite in direction. These forces act on different objects and remain equal throughout the contact time. The fact that the swimmer accelerates forward while the wall remains stationary doesn't violate this principle because the forces act on different objects with different masses. Choice D incorrectly suggests that the wall's lack of motion makes the forces unequal, confusing the effect of a force with the force itself. Remember that Newton's third law always applies—interaction forces are equal regardless of the resulting motion.
- Two ice skaters, 50 kg and 80 kg, face each other on frictionless ice and push off with their hands in contact briefly. Compare the force exerted by the 50 kg skater on the 80 kg skater to the force exerted by the 80 kg skater on the 50 kg skater.
Answer: They are equal in magnitude and opposite in direction.
This question assesses understanding of Newton's third law of motion. Newton's third law states that for every action force, there is an equal and opposite reaction force. The force exerted by the 50 kg skater on the 80 kg skater and vice versa form an action-reaction pair. These forces are equal in magnitude but opposite in direction, and they act on different objects—the two skaters. A common distractor is choice A, which incorrectly claims the heavier skater exerts a greater force due to mass, but third-law pairs are equal regardless of mass. To apply Newton's third law effectively, identify the interacting objects and remember that their mutual forces are always equal and opposite, independent of other system details.
- A student pushes a 20 N crate across a rough floor at constant speed. The student's hands remain in contact with the crate during the push. Compare the force of the student on the crate to the force of the crate on the student.
Answer: They are equal in magnitude and opposite in direction.
This question assesses understanding of Newton's third law of motion. Newton's third law states that for every action force, there is an equal and opposite reaction force. Here, the force of the student on the crate and the force of the crate on the student are an action-reaction pair. These forces are equal in magnitude but opposite in direction, and they act on different objects—the student and the crate. A common distractor is choice B, which wrongly claims the student's force is greater because the crate is moving forward, but third-law pairs remain equal regardless of motion. To apply Newton's third law effectively, identify the interacting objects and remember that their mutual forces are always equal and opposite, independent of other system details.
- A person stands on a bathroom scale in an elevator moving upward at a steady speed. The person and scale remain in contact. Compare the force of the scale on the person to the force of the person on the scale.
Answer: They are equal in magnitude and opposite in direction.
This question assesses understanding of Newton's third law of motion. Newton's third law states that for every action force, there is an equal and opposite reaction force. The force of the scale on the person and the force of the person on the scale form an action-reaction pair. These forces are equal in magnitude but opposite in direction, and they act on different objects—the scale and the person. A common distractor is choice A, which incorrectly claims the scale's force is greater because the elevator is moving upward, but third-law pairs are equal even in accelerating systems. To apply Newton's third law effectively, identify the interacting objects and remember that their mutual forces are always equal and opposite, independent of other system details.
- A 5.0 kg crate is pulled across a rough floor by a person using a horizontal rope. Consider the interaction forces between the rope and the crate at the attachment point. How does the force exerted by the rope on the crate compare to the force exerted by the crate on the rope?
Answer: The forces are equal in magnitude and opposite in direction.
This problem tests Newton's third law at the attachment point between a rope and crate. Where the rope connects to the crate, the rope exerts a forward force on the crate, and the crate exerts an equal backward force on the rope. These forces form an action-reaction pair that must be equal in magnitude and opposite in direction, regardless of friction elsewhere or the crate's motion. The forces act on different objects—the rope's force acts on the crate, while the crate's force acts on the rope. Choice C incorrectly brings in friction, which is a separate force between the crate and floor, not part of the rope-crate interaction. When analyzing Newton's third law, focus on forces at the specific interaction point and don't confuse them with other forces acting elsewhere.
- A 1200 kg car is pulled forward by a tow rope attached to a 3000 kg truck. The rope is taut and both vehicles move forward together. How does the force exerted by the rope on the car compare to the force exerted by the car on the rope?
Answer: The forces are equal in magnitude and opposite in direction.
This problem tests Newton's third law applied to a rope connecting two vehicles. At the point where the rope attaches to the car, the rope exerts a forward force on the car, and the car exerts an equal backward force on the rope. These forces form an action-reaction pair that must be equal in magnitude and opposite in direction, regardless of the masses of the vehicles or their motion. The forces act on different objects—one on the car and one on the rope. Choice A incorrectly assumes that the truck's greater mass affects the rope-car interaction, but Newton's third law applies at each interaction point independently. When analyzing connected objects, examine forces at each connection point separately and apply Newton's third law to each interaction pair.
- A 0.50 kg mass hangs motionless from a vertical spring. The spring pulls upward on the mass. Comparing the spring's force on the mass and the mass's force on the spring, which is correct?
Answer: The forces are equal in magnitude and opposite in direction.
This question tests understanding of Newton's third law for elastic forces. The spring pulls upward on the mass, and simultaneously the mass pulls downward on the spring with exactly the same magnitude force. These interaction forces are always equal in magnitude and opposite in direction, acting on different objects (spring's force on mass, mass's force on spring). The fact that the mass is motionless or that the spring is stretched doesn't change this fundamental relationship. Choice A incorrectly suggests the spring's force is larger because it's stretched, confusing the spring's extension with the interaction forces. To correctly apply Newton's third law, identify the two interacting objects and remember their forces on each other must be equal and opposite.
