Newton's Laws of Motion Quiz

Grade 9 · Science · Quiz

Challenge yourself with 10 questions covering Newton's three laws, F=ma calculations, and real-world applications.

Questions

1. A 10 kg object accelerates at 3 m/s². What net force acts on it?

   1. 0.3 N
   2. 7 N
   3. 13 N
   4. 30 N
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   Answer: 30 N

   F = ma = 10 kg × 3 m/s² = 30 N. Force is measured in Newtons (kg·m/s²).

2. Newton's First Law applies only to objects that are already moving.

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   Answer: False

   Newton's First Law applies to both moving and stationary objects. A stationary object also resists being moved — that's inertia at rest.

3. If the same force is applied to a 2 kg object and a 4 kg object, which accelerates faster?

   1. The 4 kg object
   2. The 2 kg object
   3. They accelerate equally
   4. Cannot be determined
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   Answer: The 2 kg object

   From a = F/m, a smaller mass produces greater acceleration with the same force. The 2 kg object accelerates at twice the rate of the 4 kg object.

4. The property of matter that resists changes in motion is called ___.

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   Answer: inertia

   Inertia is defined as resistance to changes in motion state. It is directly proportional to mass — heavier objects are harder to start or stop.

5. A rocket ejects gas downward and moves upward. This is an application of Newton's:

   1. First Law
   2. Second Law
   3. Third Law
   4. Law of Gravitation
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   Answer: Third Law

   Gas is pushed down (action), rocket is pushed up (reaction). Equal in magnitude, opposite in direction — Newton's Third Law in action.

6. Action-reaction force pairs described by Newton's Third Law act on the same object.

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   Answer: False

   Action-reaction pairs always act on DIFFERENT objects. The action is on one object, the reaction is on the other. If they acted on the same object, they would cancel and nothing would ever move.

7. Which scenario best demonstrates Newton's First Law?

   1. A car speeding up at a green light
   2. A hockey puck sliding on frictionless ice forever
   3. A ball falling due to gravity
   4. A rocket launching
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   Answer: A hockey puck sliding on frictionless ice forever

   With no net force (no friction), a puck in motion maintains constant velocity indefinitely — a perfect demonstration of the Law of Inertia.

8. In the formula F = ma, 'a' stands for ___.

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   Answer: acceleration

   In F = ma: F = net force (N), m = mass (kg), a = acceleration (m/s²). Any of the three can be solved when the other two are known.

9. A net force of 0 N acts on a moving object. What happens?

   1. It stops immediately
   2. It speeds up
   3. It continues at constant velocity
   4. It reverses direction
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   Answer: It continues at constant velocity

   Zero net force means no acceleration. Per Newton's First Law, an object with no net force maintains whatever velocity it already had — including zero.

10. If you double the mass of an object while keeping the force the same, what happens to acceleration?

    1. Doubles
    2. Stays the same
    3. Halves
    4. Quadruples
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    Answer: Halves

    From a = F/m, doubling m while holding F constant cuts a in half. Force and acceleration are directly proportional; mass and acceleration are inversely proportional.

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