Laws of motion

When a bus starts suddenly, the passengers are pushed back. This is an example of which of the following?

• Newton's second law

• Newton's first law

• Newton's third law

• None of above

Answer explanation

An object at rest will stay at rest and an object in motion  will stay at motion unless acted upon unbalanced force. The bus moves when an unbalanced force act on it.

What is the mass of the body if the exerted force of 10N is accelerated by 5 m/s²?

• 2.8kg

• 2.5kg

• 3.2kg

• 2kg

Answer explanation

Newton's second law of motion (f=ma) formula is used to find mass.

m=f÷a

m=10÷5

   =2kg

The ball bounces back on hitting the ground. A ball strikes the ground with certain force and the ground pushes back the ball with equal force. This is an example of which law of motion?

• Newton's second law

• Newton's third law

• Newton's first law

• None of above

Answer explanation

For every action there is an equal and opposite reaction.

The tendency of an object to stay at rest or moving at a constant speed is called…

• Velocity

• Acceleration

• Inertia

• Retardation

Newton's second law of motion relates an object acceleration to its

• Inertia

• Velocity

• Mass

• Net force

Answer explanation

The acceleration of an object is directly proportional to net force and inversely proportional to its mass.

According to Newton’s first law of motion, a moving object that is not acted on by an unbalanced force will

• Remain in motion

• Accelerate

• Stop

• Decelerate

Answer explanation

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

An ice skater at rest pushes against a sled at rest, causing both the skater and sled to move away from each other with different accelerations. This is an example best described by

• Newton’s second law of motion.

• Newton’s first law of motion.

• Newton’s third law of motion.

• None of above

Answer explanation

An ice skater at rest pushes against a sled at rest, causing both the skater and sled to move away from each other with different accelerations. this is an example best described by newton’s third law of motion: equal and opposite reaction.

A sled sliding on a flat, icy surface with a constant velocity is best described by

• Newton’s second law of motion

• Newton’s third law of motion

• Newton’s first law of motion

• None of above

Answer explanation

Newton's First Law of Motion is commonly stated as "an object in motion will remain in motion unless acted upon by an outside force." This sled is moving across the ice at the same constant speed and velocity meaning it will won't stop unless an outside force acts upon it.

If a force of 26 N is exerted on two balls A and B. Ball A mass of 0.52 kg and the ball B has mass of 0.78 kg, which ball will have the greater acceleration? 

• Ball A

• Ball B

Answer explanation

Force = Mass × Acceleration

Ball A :

26 = 0.52 × acceleration

acceleration = 26/0.52 = 50 m/s²

Ball B:

26 = 0.78 × acceleration

acceleration = 26/0.78 = 33.33 m/s²

Thus, ball with 0.52kg (ball with lesser mass) has the greater acceleration.

How does Newton’s third law explain how a rocket takes off?

• The rocket’s acceleration is positive, while the gasses acceleration is negative but the direction is the same.

• The rocket is at rest until ignition.

• The hot gasses move in one direction, while the rocket moves in the opposite direction but with equal force.

Answer explanation

In a rocket, burning fuel creates a push on the front of the rocket pushing it forward. This creates an equal and opposite push on the exhaust gas backwards.