AP Physics Classical Mechanics & Kinematics — Questions and Answers
Question 1: What is the definition of velocity?
- Speed with no direction
- Distance traveled over time
- Speed in a specified direction (Correct answer)
- Acceleration over time
Correct answer: Speed in a specified direction
Velocity is a vector quantity that describes both the speed of an object and its direction of motion. Unlike speed, which only indicates how fast an object is moving, velocity provides a complete description of its motion. For example, '60 mph' is a speed, but '60 mph north' is a velocity, specifying both magnitude and direction.
Question 2: What is the acceleration of an object in free fall near the Earth’s surface?
- 0 m/s²
- 9.8 m/s² (Correct answer)
- 10 m/s²
- None of the above
Correct answer: 9.8 m/s²
Near the Earth's surface, the acceleration of an object in free fall, neglecting air resistance, is approximately 9.8 m/s². This constant value, denoted as 'g', represents the rate at which gravity increases an object's downward velocity every second it falls. It's a fundamental constant used in many physics calculations involving gravity.
Question 3: What is the formula for calculating velocity in uniform motion?
- v = Δt / Δx
- v = Δx * Δt
- v = Δx / Δt (Correct answer)
- v = Δx + Δt
Correct answer: v = Δx / Δt
In uniform motion, velocity (v) is defined as the rate of change of displacement over time. The formula v = Δx / Δt precisely represents this relationship, where Δx is the change in position (displacement) and Δt is the change in time. This equation allows for the calculation of average velocity over an interval or instantaneous velocity if the interval is infinitesimally small.
Question 4: How does friction affect the motion of an object?
- Increases speed
- Decreases speed (Correct answer)
- Doesn’t affect speed
- Changes direction
Correct answer: Decreases speed
Friction is a force that opposes the relative motion between two surfaces in contact. When an object moves, friction acts in the opposite direction of its motion, converting kinetic energy into other forms like heat. This energy conversion results in a reduction of the object's speed or requires a continuous external force to maintain its motion.
Question 5: What is the difference between scalar and vector quantities?
- Vector quantities have magnitude only
- Scalar quantities have direction
- Scalars have magnitude, vectors have magnitude and direction (Correct answer)
- Vector quantities are always smaller
Correct answer: Scalars have magnitude, vectors have magnitude and direction
The fundamental difference between scalar and vector quantities lies in their description. Scalar quantities are fully defined by their magnitude (size) alone, such as mass, temperature, or speed. In contrast, vector quantities require both magnitude and a specific direction for their complete description, examples include velocity, force, and displacement.
Question 6: What does Newton's First Law of Motion state?
- An object needs a continuous force to move
- An object will stay at rest unless a force is applied (Correct answer)
- An object will move indefinitely without any force
- An object moves only under the influence of gravity
Correct answer: An object will stay at rest unless a force is applied
Newton's First Law of Motion, also known as the Law of Inertia, states that an object at rest will remain at rest, and an object in motion will continue in motion with the same speed and in the same direction, unless acted upon by an unbalanced external force. This means that a net force is required to change an object's state of motion, whether it's at rest or moving.
Question 7: What is the formula for kinetic energy?
- KE = mv²
- KE = 1/2 mv² (Correct answer)
- KE = m + v
- KE = 1/2 m/v²
Correct answer: KE = 1/2 mv²
Kinetic energy (KE) is the energy an object possesses due to its motion. The formula KE = 1/2 mv² quantifies this energy, where 'm' is the mass of the object and 'v' is its velocity. This equation demonstrates that kinetic energy is directly proportional to the mass and, significantly, to the square of the velocity.
Question 8: What is the principle of conservation of momentum?
- Momentum is always lost in a collision
- Momentum is conserved in an isolated system (Correct answer)
- Momentum is always gained in a collision
- Momentum can be destroyed
Correct answer: Momentum is conserved in an isolated system
The principle of conservation of momentum states that in an isolated system—one where no external forces act—the total momentum of the system remains constant. This means that the total momentum before any interaction, such as a collision, is equal to the total momentum after the interaction. Momentum can be transferred between objects within the system, but the overall sum stays the same.
Question 9: What is the relationship between force, mass, and acceleration?
- Force is inversely proportional to mass
- Force equals mass divided by acceleration
- Force equals mass times acceleration (Correct answer)
- Force is independent of mass
Correct answer: Force equals mass times acceleration
This relationship is precisely described by Newton's Second Law of Motion, famously expressed as F = ma. It states that the net force (F) acting on an object is directly proportional to its mass (m) and the acceleration (a) it experiences. Furthermore, the force acts in the same direction as the acceleration, dictating how objects change their motion.
AP Physics Classical Mechanics & Kinematics
What is the definition of velocity?