Newton's third law Transitional Reasoning Practice

Questions

1. 1.

   During a high-speed collision test, synchronized sensors record the contact forces between a moving mechanical hammer and a stationary test block. A student examining the data proposes that the force exerted by the hammer on the block must appear slightly before the block's reaction force on the hammer, reasoning that an action must precede its reaction in time. Which evaluation of the student's proposal is correct according to Newton's third law of motion?

   • A) The proposal is correct because a moving object must first initiate contact and transfer momentum before a stationary target can respond.
   • B) The proposal is correct because the material of the test block requires a measurable interval of elastic compression before generating a return force.
   • C) The proposal is incorrect because action and reaction forces are simultaneous components of a single mutual interaction, existing over the exact same time interval.
   • D) The proposal is incorrect because the reaction force only develops after the hammer completes its stroke and begins to rebound away from the block.
2. 2.

   During a tug-of-war contest on horizontal ground, Team X accelerates Team Y across the center line to win the match. A student watching the contest claims that Team X won because it exerted a greater pulling force on Team Y through the rope than Team Y exerted on Team X. Which statement correctly evaluates the student's claim according to Newton's laws of motion?

   • A) It is incorrect because the pulling forces the two teams exert on each other are always equal in magnitude; Team X wins because the ground exerts a greater horizontal friction force on Team X than on Team Y.
   • B) It is correct because the winning team must transmit a greater tension force through the rope than the reaction force it receives to accelerate the opposing team.
   • C) It is incorrect because Newton's third law applies only while both teams remain stationary; once acceleration begins, the winning team exerts a larger contact force.
   • D) It is correct because the net force accelerating the opposing team arises from an imbalance between the action force of Team X and the reaction force of Team Y.
3. 3.

   During a physics seminar on space exploration, a student argues that a rocket engine cannot accelerate in the vacuum of deep space because there is no surrounding atmosphere for the expelled exhaust gases to push against. How should this student's claim be evaluated in light of Newton's third law of motion?

   • A) The claim is correct because an external medium is necessary to provide an opposing normal force against the expanding exhaust gases.
   • B) The claim is incorrect because the rocket accelerates the exhaust gas backward, and by Newton's third law, the gas simultaneously exerts an equal forward force on the rocket.
   • C) The claim is incorrect because the rocket pushes against the gravitational field of the nearest celestial body rather than interacting with the expelled gas.
   • D) The claim is correct because Newton's third law applies only to contact forces between rigid solids rather than fluid and gas expulsions.
4. 4.

   While analyzing a sled being accelerated across horizontal snow, a student argues that the sled should not be able to speed up. The student reasons that the forward contact force exerted on the sled by the puller is matched by an equal and opposite backward force exerted by the sled on the puller, causing the two forces to cancel to zero. Which statement correctly evaluates the student's reasoning?

   • A) The reasoning is incorrect because action-reaction forces act on two different bodies, so the backward force acts on the puller and cannot cancel the forward force acting on the sled.
   • B) The reasoning is incorrect because the forward action force occurs slightly before the backward reaction force develops, creating a brief net force that initiates motion.
   • C) The reasoning is incorrect because action-reaction pairs only cancel when both interacting objects have identical masses, allowing unequal masses to generate a net force.
   • D) The reasoning is incorrect because the backward reaction force ceases to act once the sled starts moving, leaving only the forward contact force to accelerate the sled.
5. 5.

   A student mounts a strong neodymium magnet onto Cart 1 and a much weaker ceramic magnet onto an identical Cart 2, placing both carts at rest on a frictionless horizontal track with opposite poles facing. The student predicts that because Cart 1 contains a substantially stronger magnet, it will exert a greater magnetic force on Cart 2 than Cart 2 exerts on Cart 1. Which statement correctly evaluates the student's prediction according to Newton's third law?

   • A) It is correct because the magnitude of the magnetic force is determined exclusively by the pole strength of the initiating magnet.
   • B) It is incorrect because the two magnets form an action-reaction pair, exerting magnetic forces of equal magnitude on each other.
   • C) It is correct because the weaker magnet cannot project an equivalent magnetic field back onto the stronger magnet.
   • D) It is incorrect because the weaker magnet must exert a greater magnetic force to draw the stronger magnet forward.
6. 6.

   During a spacewalk in microgravity, Astronaut A firmly pushes Astronaut B, who keeps their arms relaxed and does not push back. A student claims that because Astronaut B exerted no muscular effort, only Astronaut B experiences a contact force and accelerates, while Astronaut A remains stationary. How should this student's claim be evaluated according to Newton's third law of motion?

   • A) The claim is correct because an object cannot exert a contact force on another body without actively generating muscular effort.
   • B) The claim is correct because the energy transferred by Astronaut A propagates entirely into Astronaut B without producing a counteracting force.
   • C) The claim is incorrect because the contact force exerted by Astronaut A on Astronaut B is paired with an equal and opposite force exerted by Astronaut B on Astronaut A.
   • D) The claim is incorrect because Astronaut B exerts a greater reaction force on Astronaut A to oppose the applied disturbance.
7. 7.

   A student observes a stationary physics textbook resting on a horizontal table and notes that the upward normal force exerted by the table equals the downward gravitational force exerted by Earth on the book. Because these two forces are equal in magnitude and opposite in direction, the student concludes that they form an action-reaction pair according to Newton's third law. Which evaluation of the student's conclusion is correct?

   • A) The conclusion is valid because two equal and opposite forces acting along the same line on a body always constitute an action-reaction pair.
   • B) The conclusion is valid because the textbook remains at rest, demonstrating that action-reaction pairs only occur when acceleration is zero.
   • C) The conclusion is invalid because action-reaction pairs can only exist between direct contact forces, meaning gravity cannot have a reaction partner.
   • D) The conclusion is invalid because action-reaction pairs must act on two different interacting bodies, so the reaction to Earth's gravitational force on the textbook is the textbook's gravitational force on Earth.
8. 8.

   During a vertical jump test, a calibrated force plate records an upward normal force acting on an athlete that is substantially greater than the athlete's gravitational weight during the push-off phase. Based on this measurement, a student claims that the force plate must exert a greater force on the athlete than the athlete exerts on the force plate. How should this student's claim be evaluated according to Newton's laws of motion?

   • A) The claim is incorrect because the force plate and the athlete exert forces of equal magnitude on each other; upward acceleration occurs because the normal force on the athlete exceeds the downward gravitational force acting on them.
   • B) The claim is correct because an upward acceleration can only occur when the upward contact force on the athlete exceeds the downward contact force applied by the athlete to the plate.
   • C) The claim is incorrect because the action and reaction forces act on the same object and cancel each other, leaving only the athlete's internal muscular force to produce the upward acceleration.
   • D) The claim is correct because the stationary force plate must exert a greater force than it receives to overcome the athlete's inertia and propel them off the ground.
9. 9.

   A motorized toy car is placed on a lightweight wooden plank that rests on a frictionless horizontal air table. When the car's motor is switched on, the drive wheels spin, causing the car to accelerate forward relative to the lab while the plank accelerates backward. Which statement correctly identifies the Newton's third law action-reaction pair that accounts for these observed horizontal accelerations?

   • A) The forward rotational force exerted by the motor on the axle and the opposing air drag acting against the car body.
   • B) The downward gravitational force of the car on the plank and the upward normal force of the plank on the car.
   • C) The backward horizontal friction force exerted by the wheels on the plank and the forward horizontal friction force exerted by the plank on the wheels.
   • D) The forward contact force exerted by the car chassis on the drive wheels and the backward friction force exerted by the plank on the table.
10. 10.

    During a laboratory collision investigation, a 0.50 kg cart equipped with a force sensor collides on a horizontal, frictionless track with a stationary 2.00 kg cart equipped with an identical sensor. A student hypothesizes that because the heavier cart has four times the mass and was initially at rest, it must experience a significantly greater contact force than the lighter moving cart. Which statement correctly evaluates this hypothesis based on Newton's third law of motion?

    • A) The hypothesis is incorrect because the contact forces exerted between the carts form an action-reaction pair that is always equal in magnitude and opposite in direction, regardless of mass or motion.
    • B) The hypothesis is correct because the greater inertia of the heavier cart resists acceleration more strongly, generating a larger contact force during impact.
    • C) The hypothesis is incorrect because the lighter cart was moving, so its momentum causes it to exert a greater contact force on the stationary cart.
    • D) The hypothesis is correct because the stationary cart absorbs the entire kinetic energy of the moving cart, doubling the measured interaction force.

Answers and step-by-step solutions appear after you finish the test.