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
Correct answer
Explanation
The correct answer is B, the second law. 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. Since momentum is mass times velocity, the rate of its change for a body of constant mass is mass times acceleration, which gives the equation force equals mass times acceleration.
Option A, the first law, tells us only that a body keeps its state unless an unbalanced force acts, and so defines force without measuring it. Option C, the third law, deals with the pairing of action and reaction on two different bodies. Option D belongs to a different branch of the subject altogether. The second law also gives the definition of the newton, which is the force that gives a mass of one kilogram an acceleration of one metre per second squared.
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 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.
Read the full explanation →A passenger standing in a moving bus falls forward when the bus stops suddenly. This is due to
- A.Inertia of rest
- B.Inertia of motion
- C.Inertia of direction
- D.Centripetal force
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While the bus is moving, the passenger's whole body moves with it. When the brakes are applied, the feet stop along with the floor of the bus, but the upper body tends to keep moving forward at the same speed, and the passenger is thrown forward.
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