Science 8 (1st Qtr.) - Review

Which of the following is the constant value for the Earth's force of gravity

• 8.87 m/s²

• 1.6 m/s²

• 9.8 m/s²

• 10.44 m/s²

Answer explanation

The constant value for the Earth's force of gravity is approximately 9.8 m/s². This value is widely accepted and used in physics to represent the acceleration due to gravity at Earth's surface.

A book is sitting on a dashboard of a car that's stopped at a traffic light. As the car starts to move forward, the book slides off the dashboard. Pick the most correct explanation.

• The object had inertia.

• A supernatural force took over.

• There was grease on the dashboard.

• Air resistance made the book move backward.

Answer explanation

The book slid off the dashboard because it had inertia, which is the tendency of an object to resist changes in its state of motion. When the car accelerated, the book remained at rest momentarily, causing it to fall.

1. Which of the following has the greatest inertia?

• car

• bus

• bike

• airplane

Answer explanation

Inertia is the resistance of an object to changes in its motion. An airplane, being the largest and heaviest among the options, has the greatest mass, thus it has the greatest inertia compared to a car, bus, or bike.

1. Which of the following equations represent Newton’s second law of motion?

• a = Fm

• a = F

• m = aF

• F = ma

Answer explanation

The correct representation of Newton's second law of motion is F = ma, where F is force, m is mass, and a is acceleration. This equation shows that force is the product of mass and acceleration.

Which of the following is the BEST example of the Newton's Third Law?

• A rocket taking off from earth which pushes gases in one direction and the rocket in the other.

• A rocket sitting on the ground preparing for take-off but it needs an outside force to overcome its inertia of a non-moving object.

• A rocket that is accelerating through space and exerts a great amount of force because its mass and acceleration is so large.

• Both B and C.

Answer explanation

Both B and C illustrate Newton's Third Law, which states that for every action, there is an equal and opposite reaction. B describes overcoming inertia, while C highlights the force exerted during acceleration.

How much net force is needed for a 15kg object to accelerate up to 2.5 m/s²?

• 37 N

• 36 N

• 37.5 N

• 36.5 N

Answer explanation

To find the net force, use F = ma. Here, m = 15 kg and a = 2.5 m/s². Thus, F = 15 kg * 2.5 m/s² = 37.5 N. Therefore, the correct answer is 37.5 N.

Which of the following factors are related to work?

• mass and acceleration

• force and acceleration

• force and displacement

• mass and displacement

Answer explanation

Work is defined as the product of force and displacement in the direction of the force. Therefore, the correct choice is 'force and displacement', as these factors directly relate to the concept of work.

An object was displaced up to 4.5 meters after a person carried it, and exerting a force of 3.25 N. How much work was done?

• 14.63 J

• 14 J

• 14.61 J

• 14.5 J

Answer explanation

Work is calculated using the formula: Work = Force x Distance. Here, Work = 3.25 N x 4.5 m = 14.625 J, which rounds to 14.63 J. Thus, the correct answer is 14.63 J.

Which of the following statements about negative work is TRUE?

• The object slows down.

• The object moves in the opposite direction.

• There is no such thing as negative work.

• The force applied to the object varies in magnitude.

Answer explanation

Negative work occurs when the force applied to an object opposes its motion, causing it to slow down. Therefore, the statement 'The object slows down' is true.

Which group usually wins in a tug–of–war?

• depends on the force applied

• the group that pulls the rope harder

• the group that pushes the ground harder

• neither of the group will win the tug-of-war

Answer explanation

In a tug-of-war, the group that pushes the ground harder generates more friction and stability, allowing them to pull the rope more effectively. Thus, the correct answer is the group that pushes the ground harder.