Grade 8 Physics Reviewer Quarter 1

Which of the following describes the motion of an object if the forces acting on it are unbalanced?

• The object will stay in place.

• The object will accelerate in the direction of the net force.

• The object will move in a straight line at a constant speed.

• The object will continue to move in its current direction at a constant speed.

Answer explanation

When forces are unbalanced, there is a net force acting on the object. According to Newton's second law, this net force causes the object to accelerate in the direction of that force.

Which of the following correctly describes a ball resting on the table?

• The ball will fall.

• The ball is weightless.

• The net force on the ball is zero.

• No forces are acting on the ball.

Answer explanation

The ball is at rest on the table, meaning the forces acting on it are balanced. The gravitational force pulling it down is equal to the normal force from the table pushing it up, resulting in a net force of zero.

Newton's First Law states that an object at rest will stay at rest unless acted upon by a force. How would this law apply to a book lying on a table?

• The book will start moving on its own.

• The book will move if the table shakes.

• The book will eventually fall off the table by itself.

• The book will remain stationary unless a force is applied.

Answer explanation

According to Newton's First Law, the book will remain stationary on the table unless a force, such as a push or pull, is applied to it. This means it will not move on its own or fall off without an external force.

In Newton's First Law of motion, what will be the effect of a force applied to an object at rest?

• The object will start rotating.

• The object will remain at rest.

• The object will change its state of motion.

• The object will increase its velocity without changing direction.

Answer explanation

According to Newton's First Law, an object at rest will remain at rest unless acted upon by a force. Therefore, applying a force will change its state of motion, making the correct choice "The object will change its state of motion."

According to Newton's Second Law of Motion, what is the relationship between net force and acceleration?

• Acceleration is equal to the net force.

• Acceleration is independent of the net force.

• Acceleration is directly proportional to the net force.

• Acceleration is inversely proportional to the net force.

Answer explanation

According to Newton's Second Law, acceleration (a) is directly proportional to the net force (F) acting on an object, expressed as F = ma. Thus, when net force increases, acceleration increases, confirming the correct choice.

If the net force acting on an object is doubled, what happens to its acceleration, assuming the mass remains constant?

• Acceleration is halved.

• Acceleration is doubled.

• Acceleration is quadrupled.

• Acceleration remains unchanged.

Answer explanation

According to Newton's second law, F = ma. If the net force (F) is doubled and mass (m) remains constant, acceleration (a) must also double to maintain the equation. Therefore, acceleration is doubled.

What does Newton's 3rd Law of Motion state?

• Force equals mass times acceleration.

• For every action, there is an equal and opposite reaction.

• Objects at rest stay at rest unless acted upon by a force.

• An object in motion stays in motion unless acted upon by an external force.

Answer explanation

Newton's 3rd Law of Motion states that for every action, there is an equal and opposite reaction. This means that forces always occur in pairs, making this the correct choice among the options provided.

Which of the following is an example of Newton's 3rd Law of Motion?

• A car accelerates when gas is applied.

• An apple falls from a tree due to gravity.

• A ball thrown upwards falls back to the ground.

• A person pushes against a wall, and the wall pushes back with equal force.

Answer explanation

Newton's 3rd Law states that for every action, there is an equal and opposite reaction. When a person pushes against a wall, the wall exerts an equal force back, exemplifying this law. The other options do not illustrate this principle.

Which of the following conditions must be consider for work to be done?

• An object is moving, but no force is applied.

• A force is applied, and the object remains stationary.

• A force is applied in a direction perpendicular to the object's motion.

• A force is applied, and the object moves in the direction of the force.

Answer explanation

For work to be done, a force must be applied and the object must move in the direction of that force. This means that the force causes displacement, which is essential for work to occur.

If a person pushes a wall with all their strength and the wall does not move, how much work is done?

• Maximum work is done.

• No work is done.

• Some work is done due to the force applied.

• It depends on the strength of the person.

Answer explanation

No work is done when a force is applied but there is no movement. Work is defined as force applied over a distance. Since the wall does not move, the distance is zero, resulting in zero work done.