Unit 3 Review

Slamming on the brakes in a moving car makes a passenger move forward against his or her seat belt because:

• The passenger has the inertia to keep moving forward.

• The passenger is being pushed by the seats of the car.

• The passenger is better able to stop themselves in this manner.

• The passenger has an equal and opposite force supporting their weight.

Answer explanation

The correct answer is that the passenger has the inertia to keep moving forward. Inertia is the tendency of an object to resist changes in its state of motion, so when the car stops suddenly, the passenger continues moving forward.

How long will an object remain at rest according to Newton's First Law of Motion?

• It can't rest

• Until noon

• Until an unbalanced force occurs

• As long as there are unbalanced forces acting on it

Answer explanation

According to Newton's First Law of Motion, an object at rest will remain at rest until an unbalanced force occurs. This means that without such a force, the object will not change its state of rest.

Why is it harder to push a van filled with bowling balls than it is to push a van filled with basketballs?

• The mass of the car is greater than the mass of the basketballs.

• The mass of the bowling balls is greater than the mass of the basketballs.

• The van with the basketballs is bigger than the van with the bowling balls.

• It should be equally as hard to push the two vans.

Answer explanation

The mass of the bowling balls is greater than the mass of the basketballs, making it harder to push the van filled with bowling balls. More mass means more force is needed to overcome inertia.

You are holding a bowl of hot soup while standing in the kitchen. As you begin to move, the soup spills out of the bowl. Upon reflection, you realize that:

• The soup spilled because of air resistance.

• If you had traveled faster, this wouldn't have happened.

• The soup wanted to stay where it was, but you moved the bowl.

• The soup and the bowl act as one body with the same velocity.

Answer explanation

The soup spilled because, according to Newton's first law, it tends to remain at rest while you moved the bowl. The correct choice highlights that the soup wanted to stay in place as you changed the bowl's position.

Which of these is an example of Newton's Second Law, F=ma?

• A tug of war where both sides pull equally, and the rope doesn't move.

• A wide receiver using his hands to stop and catch a football thrown by the quarterback.

• A car traveling on a straight part of the highway with cruise control set at constant velocity.

• A book pushing down on the desk where it is resting.

Answer explanation

In a tug of war where both sides pull equally, the forces are balanced, resulting in no acceleration (F=ma). This illustrates Newton's Second Law, as the net force is zero and the rope does not move.

You pull a wagon with your younger sister in it. Which of these actions would increase the rate at which you can pull the wagon?

• Pull the wagon with less force

• Pull the wagon with more force

• Have your sister push down on the wagon

• Put another of your siblings in the wagon

Answer explanation

Pulling the wagon with more force increases the acceleration according to Newton's second law (F=ma). More force results in greater acceleration, allowing you to pull the wagon faster.

A wheelbarrow is experiencing two forces: one is pushing 5N east and another 5N west. What is true about the motion of the wheelbarrow?

• It isn't moving

• It is accelerating

• It is slowing down

• Its speed is constant

Answer explanation

The wheelbarrow experiences equal and opposite forces (5N east and 5N west), resulting in a net force of 0N. Therefore, it isn't moving, as there is no unbalanced force to cause acceleration.

Pat measures a small rubber ball and makes 3 other balls of the same diameter from lead, foam, and wood. Which has the greatest inertia?

• rubber ball

• lead ball

• foam ball

• wood ball

Answer explanation

Inertia depends on mass; the lead ball, being denser than rubber, foam, and wood, has the greatest mass for the same volume. Therefore, the lead ball has the greatest inertia.

When you push a boat off from the dock, you are demonstrating Newton's 3rd Law of Motion. It simply states that for every action, there is an equal and opposite _______________?

• Motion

• Change

• Reaction

• Push

Answer explanation

The correct answer is 'Reaction'. Newton's 3rd Law states that for every action, like pushing a boat, there is an equal and opposite reaction, which is the force exerted back on you by the boat.

A car is moving at a constant speed on a straight road. What can be said about the forces acting on the car?

• The forces are balanced.

• The car is accelerating.

• The forces are unbalanced.

• There is no force acting on the car.

Answer explanation

Since the car is moving at a constant speed, the net force acting on it must be zero. This means that all forces are balanced, preventing any acceleration. Therefore, the correct choice is that the forces are balanced.