Force, Motion, and Friction Flashcards

An object is pushed across a rough, horizontal surface at a constant velocity. Which of the following statements is true regarding the forces acting on the object?

Answer: The force of friction is equal to the applied force.

According to Newton's First Law of Motion, an object moving at a constant velocity has zero acceleration. This means the net force acting on it is zero. Therefore, the applied force pushing the object forward must be equal in magnitude and opposite in direction to the force of kinetic friction resisting the motion.

A person is trying to push a heavy crate across a floor but it does not move. Which type of friction is preventing the crate from moving?

Answer: Static friction

Static friction is the force that opposes the initiation of motion between two surfaces in contact. Since the crate is not moving despite the applied force, static friction is the force that is counteracting the push. Kinetic friction applies only when an object is already in motion.

If the force applied to an object is doubled, while its mass remains constant, what is the effect on its acceleration?

Answer: It is doubled.

This question relates to Newton's Second Law of Motion, which states that Force = Mass × Acceleration (F=ma). If the mass (m) is constant, acceleration (a) is directly proportional to the force (F). Therefore, if the force is doubled, the acceleration must also double to maintain the equality.

A block is sliding down a frictionless ramp. Which of the following forces is responsible for its acceleration down the ramp?

Answer: The component of gravity parallel to the ramp's surface.

The force of gravity acts vertically downwards. On an inclined plane, this force can be resolved into two components: one perpendicular to the ramp and one parallel to it. The perpendicular component is balanced by the normal force. The parallel component is unbalanced (since there is no friction) and pulls the object down the ramp, causing it to accelerate.

Which of the following actions would increase the kinetic friction between a moving sled and the snowy ground?

Answer: Adding more weight to the sled.

The force of kinetic friction is calculated as the product of the coefficient of kinetic friction and the normal force. The normal force is equal to the weight of the sled (mass times gravity). By adding more weight to the sled, you increase the normal force, which in turn increases the force of kinetic friction.

According to Newton's Third Law of Motion, if a person pushes against a wall with a force of 50 Newtons, what is the force exerted by the wall on the person?

Answer: 50 Newtons in the opposite direction.

Newton's Third Law of Motion states that for every action, there is an equal and opposite reaction. The person's push on the wall is the 'action'. The 'reaction' is the wall pushing back on the person with an equal force of 50 Newtons but in the opposite direction.