Forces, Motion, and Interactions Flashcards

A soccer ball with a mass of 0.45 kg is kicked by a player. The ball accelerates at 20 m/s². What is the net force applied to the ball?

Answer: 9 N

According to Newton's Second Law of Motion, the net force on an object is the product of its mass and acceleration (F=ma). To find the force, multiply the mass (0.45 kg) by the acceleration (20 m/s²), which equals 9 N.

A student is riding a skateboard at a constant velocity. Suddenly, the skateboard hits a crack in the sidewalk and stops, but the student continues to move forward. Which of the following principles best explains why the student continues to move forward?

Answer: Inertia (Newton's First Law)

This is an example of Newton's First Law of Motion, also known as the law of inertia. The student's body was in motion and tends to remain in motion with the same velocity, even after the skateboard was stopped by an external force.

Which of the following scenarios describes an object experiencing a net unbalanced force?

Answer: A satellite orbiting Earth at a constant speed.

A net unbalanced force causes acceleration, which is a change in velocity (speed or direction). A satellite orbiting Earth is constantly changing its direction, so it is continuously accelerating due to the unbalanced force of gravity, which acts as a centripetal force.

A swimmer pushes backward on the water with their hands. In response, the water pushes the swimmer forward. This is a direct application of which principle?

Answer: The Law of Action-Reaction (Newton's Third Law)

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. The swimmer's push on the water is the 'action,' and the water pushing back on the swimmer with an equal and opposite force is the 'reaction,' which propels the swimmer forward.

According to Newton's Law of Universal Gravitation, the gravitational force between two objects is inversely proportional to the square of the distance between them. If the distance between two planets is doubled, what happens to the gravitational force between them?

Answer: It is reduced to one-fourth of its original value.

The Law of Universal Gravitation follows an inverse square law. This means if the distance (r) is doubled, the new force is proportional to 1/(2r)², which equals 1/4r². Therefore, the force becomes one-fourth of its original value.

A student pushes a heavy box across a rough floor but the box does not move. Which statement best explains this situation?

Answer: The force of static friction is equal to and opposite the student's pushing force.

For the box to remain stationary, the net force must be zero. The student's push is an applied force. This force is being counteracted by an equal and opposite force of static friction from the floor. Until the student's push exceeds the maximum static friction, the box will not move.