In this worksheet, we will practice applying Newton's third law of motion to calculate the forces acting on pairs of mutually attracting or repelling objects.

**Q2: **

When starting a race, a 55.0-kg-mass sprinter exerts an average force of 635 N backwards on the ground for 0.560 s.

What is the sprinter’s speed after the acceleration?

- A 7.55 m/s
- B 3.50 m/s
- C 12.4 m/s
- D 6.47 m/s
- E 16.2 m/s

How far does the sprinter move during the acceleration?

- A 1.81 m
- B 2.50 m
- C 1.25 m
- D 0.996 m
- E 3.50 m

**Q3: **

A lorry collides with a car and, during the collision, the net force on each vehicle is equal to the force exerted by the other vehicle. The mass of the car is kg and the mass of the lorry is kg. The magnitude of the lorry’s acceleration is 8.63 m/s^{2}. Find the magnitude of the car’s acceleration.

- A
55.7 m/s
^{2} - B
25.5 m/s
^{2} - C
18.5 m/s
^{2} - D
37.8 m/s
^{2} - E
12.4 m/s
^{2}

**Q4: **

Which of the following is true?

- AA rocket taking off exerts a force on Earth equal in magnitude to the force Earth exerts on it.
- BEarth exerts a force due to gravity on your body and your body exerts a smaller force on Earth because your mass is smaller than the mass of Earth.
- CAn aeroplane cruising at a constant speed is not affected by gravity.
- DThe Moon orbits Earth because Earth exerts a force on the Moon and the Moon exerts a force equal in magnitude and opposite in direction on Earth.

**Q5: **

Which force causes a boat to move forward when someone rows it?

- AThe frictional force between the boat and the water.
- BThe frictional force between the oars and the water.
- CThe force of gravity acting on the oars.
- DThe force of the oars pushing against the water.

**Q6: **

What is Newton’s third law of motion also known as?

- Athe law of force
- Bthe law of inertia
- Cthe law of gravitational attraction
- Dthe law of action-reaction
- Ethe law of conservation of energy

**Q7: **

A sports car of mass 550 kg
collides with a truck of mass
2 200 kg, and,
during the collision, the net force on each vehicle is the force exerted by the
other. The magnitude of the truck’s acceleration is
10 m/s^{2}. What
is the magnitude of the sports car’s acceleration?