Newton's Laws: 26 MCQs with answers

Newton's first law

Newton's first law, also called the law of inertia, describes the tendency of objects to resist changes in their state of motion unless an unbalanced force acts on them.

$F = ma$

Newton's second law states that the net force acting on an object is equal to the mass of the object multiplied by its acceleration, $F = ma$.

10 N

Newton's third law states that for every action, there is an equal and opposite reaction. So the wall exerts a force of 10 N back on you.

First law

The first law is called the law of inertia because it describes the resistance of an object to changes in its motion.

True

This is the exact statement of Newton's third law.

An object at rest will stay at rest, and an object in motion will stay in motion unless acted upon by an unbalanced force.

The correct option describes Newton's first law, which emphasizes the concept of inertia.

The acceleration of an object is proportional to the net force acting on it and inversely proportional to its mass.

The correct option summarizes Newton's second law, relating force, mass, and acceleration.

A book sitting on a table.

The correct option shows an object at rest, illustrating the concept of inertia as defined by Newton's first law.

Forces can exist even if no motion occurs.

The correct option indicates that forces can act on objects regardless of their state of motion.

Mass and acceleration are inversely proportional.

The correct option reflects that as mass increases, acceleration decreases for a given force.

5 N

The correct option illustrates Newton's third law, which states that forces are equal and opposite.

Forces that cause a change in an object's motion.

The correct option defines unbalanced forces as those that result in a change in motion.

Newton (N)

The correct option identifies the Newton as the standard unit of force in SI.

A book resting on a table.

The correct option shows an object at rest with no net force acting on it.

The rate of change of velocity of an object.

The correct option defines acceleration as the change in velocity over time.

An object continues in its state of rest or uniform motion unless acted upon by a net external force.

Newton's first law describes inertia: without a net external force, an object maintains its velocity (which may be zero).

$5\ \text{m/s}^2$

Using Newton's second law, $a = F/m = 20\ \text{N} / 4\ \text{kg} = 5\ \text{m/s}^2$.

Halve

From $a = F/m$, acceleration is inversely proportional to mass. Doubling mass halves acceleration when force is constant.

The force of the book on the table and the force of the table on the book

Newton's third law pairs are action-reaction forces between two objects. The book pushes down on the table, and the table pushes up on the book with equal magnitude.

Mass

Mass is a scalar quantity (only magnitude), while force, acceleration, and velocity are vectors (magnitude and direction).

$6\ \text{N}$

Using $F = ma$, $F = 2\ \text{kg} \times 3\ \text{m/s}^2 = 6\ \text{N}$.

A ball rolling on a frictionless surface continues at constant velocity.

Newton's first law states that an object in motion continues at constant velocity unless acted upon by a net force. A frictionless surface approximates no net force.

Act on different objects

Action-reaction pairs act on different objects, so they do not cancel each other. They are equal in magnitude and opposite in direction.

$5\ \text{kg}$

From $F = ma$, $m = F/a = 10\ \text{N} / 2\ \text{m/s}^2 = 5\ \text{kg}$.

False

According to Newton's first law, a net force causes a change in velocity (acceleration). Constant velocity requires zero net force.

Momentum

In this form, $p$ represents linear momentum ($p = mv$), and the net force equals the rate of change of momentum.