According to Newton's third law, action and reaction
- A.Act on the same body and cancel each other
- B.Act on two different bodies and do not cancel each other
- C.Are unequal in magnitude
- D.Act in the same direction
Correct answer
Explanation
The correct answer is B. The third law says that to every action there is an equal and opposite reaction, and the crucial point is that the two forces act on two different bodies. A swimmer pushes the water backward and the water pushes the swimmer forward; the first force acts on the water and the second on the swimmer.
Option A states the popular misunderstanding: forces can cancel only when they act on the same body, so if action and reaction acted on the same body nothing would ever move. Option C contradicts the law, which insists the two are equal in magnitude. Option D reverses the direction; they are exactly opposite. Other standard examples are the recoil of a gun, the movement of a rocket as gases are pushed out behind it, and the backward push of the ground felt when walking.
Read the full article: Motion, Force and Newton's Laws: Formulas and Facts
Practice Questions
View allNewton's first law of motion is also known by which name?
- A.Law of inertia
- B.Law of momentum
- C.Law of action and reaction
- D.Law of gravitation
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The first law states that a body continues in its state of rest or of uniform motion in a straight line unless an unbalanced external force acts on it, which is exactly the property called inertia.
Read the full explanation →Which of the following is a vector quantity?
- A.Distance
- B.Speed
- C.Displacement
- D.Time
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It is the shortest distance from the starting point to the finishing point together with the direction of that straight line, so it has both magnitude and direction and is therefore a vector.
Read the full explanation →The equation force equals mass multiplied by acceleration follows from which law of motion?
- A.First law
- B.Second law
- C.Third law
- D.Law of conservation of energy
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It states that the rate of change of momentum of a body is proportional to the applied force and takes place in the direction of the force.
Read the full explanation →The recoil of a gun when a bullet is fired is explained by the conservation of which quantity?
- A.Energy
- B.Linear momentum
- C.Mass
- D.Electric charge
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Before firing, the gun and the bullet are at rest, so the total momentum of the system is zero.
Read the full explanation →What is the SI unit of momentum?
- A.Newton
- B.Joule
- C.Kilogram metre per second
- D.Newton per second
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Momentum is the product of mass and velocity, so its unit is the unit of mass multiplied by the unit of velocity, that is kilogram multiplied by metre per second.
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