Gravity and Kinetic Energy

• diameter and theory

• difference and trajectory

• distance and time

• divisor and term

Answer explanation

The speed formula can be defined as the rate (time) at which an object covers some distance. Distance is how far something moves (miles, kilometers, feet, etc.), and time is how long it takes to move that far (hours, seconds, days, etc.). We can use the speed formula to calculate the distance or time by substituting the known values in the formula and solve for the missing variable.

Which of the following best describes Newton's Third Law of Motion?

• An object at rest stays at rest unless acted upon by an external force.

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

• The acceleration of an object is directly proportional to the net force acting on it.

• The force of gravity is inversely proportional to the square of the distance between two objects.

Answer explanation

Newton's Third Law states that for every action, there is an equal and opposite reaction, meaning forces always occur in pairs. The other options describe different laws or principles.

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Kai is riding his bicycle, and he decides to pedal faster, doubling his speed. How does this change affect the kinetic energy of the bicycle?

• It remains the same.

• It doubles.

• It triples.

• It quadruples.

Answer explanation

Kinetic energy (KE) is given by the formula KE = 1/2 mv². If Kai doubles his speed (v), the new KE becomes 1/2 m(2v)² = 2mv², which is 4 times the original KE. Thus, the kinetic energy quadruples.

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Which of the following scenarios best illustrates the concept of potential energy?

• A car accelerating on a highway.

• A book resting on a shelf.

• A ball rolling down a hill.

• A person running a marathon.

Answer explanation

A book resting on a shelf has potential energy due to its position above the ground. This energy can be converted to kinetic energy if the book falls, unlike the other scenarios which involve motion.

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• 0.25 km

• 0.25 hours

• 4 km

• 4 hours

Charlotte and Oliver are observing the gravitational force between two planets. Which of the following best describes the gravitational force between these two planets?

• It is always attractive and depends on the masses of the objects and the distance between them.

• It is always repulsive and depends on the masses of the objects and the distance between them.

• It is always attractive and independent of the distance between the objects.

• It is always repulsive and independent of the masses of the objects.

Answer explanation

The gravitational force is always attractive, pulling masses together. It depends on the masses of the objects and the distance between them, as described by Newton's law of universal gravitation.

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Which of the following is evidence that fields exist between objects exerting forces on each other even though the objects are not in contact?

• A magnet attracting a paperclip from a distance.

• A car moving on a road.

• A person lifting a box.

• A ball rolling on the ground.

Answer explanation

A magnet attracting a paperclip from a distance demonstrates the existence of a magnetic field, which exerts a force without direct contact. This is clear evidence of fields acting between objects.

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In an experiment, a charged balloon is brought near small pieces of paper, causing them to move. What does this demonstrate about electric fields?

• Electric fields only exist when objects are in contact.

• Electric fields can exert forces over a distance.

• Electric fields have no effect on neutral objects.

• Electric fields are weaker than gravitational fields.

Answer explanation

This demonstrates that electric fields can exert forces over a distance, as the charged balloon influences the neutral paper pieces without direct contact.

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This force holds us to earth’s surface.

• friction

• mass

• weight

• tension

Answer explanation

The force that holds us to the Earth's surface is weight, which is the gravitational pull on an object's mass. Friction, mass, and tension do not directly relate to this force.

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When a roller coaster is at the bottom of a hill it has

• high potential energy

• high kinetic energy

• low kinetic energy

• equal amounts of kinetic and potential energy

Answer explanation

At the bottom of a hill, a roller coaster has converted potential energy into kinetic energy, resulting in high kinetic energy. This is why the correct answer is 'high kinetic energy'.

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