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11th grade Newton's third law: force pairs worksheet

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Newton's third law: force pairs

Grade 11 Science Worksheet - Challenge Me

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Circle the best answer, or write your answer on the line.

  1. A 1.5 kg cart at 2 m/s hits a 0.5 kg cart at rest and they stick. The contact lasts 0.1 s. What average force acts on the 0.5 kg cart, Ari?

  2. A 2 kg cart at 3 m/s hits a 1 kg cart at rest and they stick. The contact lasts 0.05 s. What average force acts on the 1 kg cart, Bo?

  3. A 0.8 kg cart at 1.5 m/s hits a 1.2 kg cart at rest and they stick. The contact lasts 0.2 s. What average force acts on the 1.2 kg cart, Esme?

  4. The two sensors do not give identical readings in any trial. Do the data contradict the third law, Luz?

    • Yes: the readings differ, so the forces were not equal
    • No: the gaps are 0.3 N or less, within the sensors' 0.5 N accuracy
    • Yes: cart B read higher in two trials, so B pushed harder
    • No: the third law requires the readings to match to the last digit

  5. Milo says a rocket's thrust and the exhaust's force are equal and opposite, so the rocket cannot accelerate. Agree?

    • Agree: the thrust works because the exhaust pushes the air
    • Disagree: the forces act on different objects, the rocket and the gas
    • Agree: equal and opposite forces cancel, so the rocket stays put
    • Disagree: the gas pushes harder than the rocket, so it moves forward faster

  6. Block A rides on block B without slipping, and both accelerate at 3 m/s² on a smooth table. Noah says block A pushes nothing on block B, since A just rides along. Using the diagrams, agree or disagree?

    • Disagree: A needs 6 N from B, so A pushes back on B with 6 N
    • Disagree: A pushes B with 2 N, its mass times 1 m/s²
    • Agree: the hand's 18 N is the one force that acts on block B
    • Agree: a block that rides along without slipping exerts no force on the other

  7. The contact lasts 0.050 s. Pia says the heavier cart in the table gains more momentum than the lighter cart loses. Agree or disagree?

    • Disagree: B gains 1.25 kg·m/s, exactly what A loses
    • Disagree: A loses 2.5 kg·m/s, twice what B gains
    • Agree: B is twice as heavy, so it gains twice as much
    • Agree: B ends faster than A did, so it gained more

  8. A 10 N push drives a 2 kg block into a 3 kg block; only the 3 kg block feels 4 N of friction. How hard do the blocks push each other, Ren?

    • 3.6 N, the 3 kg block's mass times its acceleration
    • 6 N, from 10 N shared by mass, ignoring the friction
    • 2.4 N, the net force on the 2 kg block alone
    • 7.6 N, since the 3 kg block needs 3 × 1.2 N plus 4 N

  9. Team A is on ice and slips at a rope tension of 150 N. Team B is on rough pavement, and its feet hold. Which way does the contest go, Tala?

    • Team A wins, since the ice lets its team pull the rope more easily
    • Team B slides toward team A, since B pulls with the larger force
    • Team A slides toward team B, since only B's feet can hold 150 N
    • Neither team moves, since the rope forces on them are equal and opposite

  10. A 50 kg skater on smooth ice throws a 2 kg ball forward at 5 m/s. How fast does the skater move backward, Zee?

    • 0.04 m/s, since the mass ratio must be squared
    • 0.1 m/s, since the skater's mass is spread over 100 kg of load
    • 0.2 m/s, since the skater gets the same momentum as the ball
    • 5 m/s, since the skater and ball feel equal and opposite forces
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11th grade Newton's third law: force pairs worksheet – printable
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About this worksheet

Newton's third law: force pairs. Every version has 10 questions, and the answer key prints on the second page.

What your child will learn

  • I can name a force's partner by swapping the objects (A on B gives B on A). I can tell a pair (two objects) from balanced forces (one object), such as a book's weight and the table's push.
  • I can explain why pair forces never cancel: they act on different objects, so each object accelerates from its own force.
  • I can use equal pair forces with different masses: a = F ÷ m for each cart, and m₁a₁ = m₂a₂.
  • I can explain propulsion: a drone pushes air down and the air pushes it up (thrust = m(g + a) when accelerating). Balloons and fan carts work the same way.

Standard: supports HS-PS2-1

Words to know

force pair: Two equal, opposite forces that two objects exert on each other

partner force: The other force in a pair: B on A for A on B

balanced forces: Forces on one object that add to zero

thrust: The push from air or gas that moves a drone or balloon

system: The objects you choose to study together

Common mistakes

Your child used the wrong share of the push. Block A is pushed by the hand and also pushes block B, so block B's force depends on B's mass over the total mass.

Your child split the push in half. The blocks share the push in proportion to their masses, not equally.

Your child said a force pair cancels. The two forces act on different objects, so each one changes its own object's motion.

Questions parents ask

What is the most common mistake with newton's third law: force pairs?

Your child used the wrong share of the push. Block A is pushed by the hand and also pushes block B, so block B's force depends on B's mass over the total mass.

Are these 11th grade science worksheets free to print?

Yes. All 6 printable versions at each level are free to print, with the answer key, and no account is needed.

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