Newton's third law: force pairs
Grade 11 Science Worksheet - Challenge Me
Circle the best answer, or write your answer on the line.
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?
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?
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?
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
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
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
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
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
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
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