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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

NameDate

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

  1. A 1600 kg truck tows a 400 kg trailer. The road pushes the truck 5000 N forward; the trailer meets 400 N of resistance. How hard does the coupling pull the trailer, Ari?

  2. A 2000 kg truck tows a 1000 kg trailer. The road pushes the truck 7500 N forward; the trailer meets 600 N of resistance. How hard does the coupling pull the trailer, Bo?

  3. A 900 kg truck tows a 300 kg trailer. The road pushes the truck 3000 N forward; the trailer meets 300 N of resistance. How hard does the coupling pull the trailer, Esme?

  4. Block A rides on block B without slipping, and both accelerate at 3 m/s² on a smooth table. Using the diagrams, which force is the third-law partner of block B's 6 N friction on block A, Jun?

    • The 6 N net force on block A, pointing forward
    • Block A's 6 N friction on block B, pointing backward
    • The hand's 18 N push on block B, pointing forward
    • Block A's weight pulling it down onto block B

  5. Read this first

    Use this

    Two free-body diagrams side by side (example data). truck (1000 kg): push from the road 3000 N forward; pull from the coupling 1200 N backward. trailer (500 kg): pull from the coupling 1200 N forward; road resistance 300 N backward. The truck tows the trailer along a level road.

  6. Which force is the third-law partner of the coupling's 1,200 N pull forward on the trailer, Kira?

    • The 300 N road resistance backward on the trailer
    • The 900 N net force on the trailer, pointing forward
    • The trailer's 1,200 N pull backward on the truck
    • The road's 3,000 N push forward on the truck

  7. Treat the truck and trailer together as one system. The truck and trailer accelerate at 1.8 m/s². Taking the truck and trailer as one system, which forces set its acceleration, Luz?

    • The road's push and the resistance; the coupling cancels inside
    • The four forces together, since the coupling pulls on each vehicle
    • The 1,200 N coupling pull, since it joins the two vehicles together
    • The road's 3,000 N push alone, since the resistance is small

  8. A horse pulls a cart, and the cart pulls back on the horse equally. Why does the horse-and-cart system speed up, Milo?

    • The cart's pull is a delayed reaction, so the horse gets ahead
    • The two pulls cancel each other, so the system moves at constant speed
    • The ground pushes the hooves forward more than friction drags back
    • The horse pulls harder on the cart than the cart pulls on the horse

  9. The rope tension is 400 N. Team A's feet get 400 N of friction and hold. Team B's feet can get at most 380 N. Which team wins, Noah?

    • Team A: 400 N pulls team B, but its feet give 380 N, so B slides
    • Both teams stay put, since each rope end carries the same 400 N
    • Team B, since a smaller friction means it pulls harder on the rope
    • Team B, since the rope pulls team A with 400 N but team B with 380 N

  10. A 2 kg cart at 3 m/s hits a 4 kg cart at rest and they stick, moving off at 1 m/s. How do the carts' changes in momentum compare, Tala?

    • The heavier cart gains more, since it is the heavier cart
    • Both are zero, since the momentum of the system is unchanged
    • Equal in size and opposite in direction, 4 kg·m/s each
    • The 2 kg cart loses 6 kg·m/s and the 4 kg cart gains 4

  11. A cart carries a fan blowing forward at a sail fixed on the same cart. Every bit of that air hits the sail. Does the cart speed up, Zee?

    • No: the fan and sail forces are inside the cart and cancel
    • Yes: the fan pushes air back, which pushes the cart forward
    • Yes: the air pushes the sail forward, so the cart is pushed ahead
    • No: the sail is too small for the air to push it
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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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