MCAT - Chem/Phys Foundations:: Physics

Velocity, describing an object's motion, differs from speed in that velocity is a:

- **A)** Vector quantity, meaning it has both a magnitude (numerical speed) AND a specified direction, while speed is a scalar quantity (magnitude only, with no directional component)
- **B)** Scalar quantity with no directional component, identical to speed
- **C)** Quantity that can never be negative, unlike speed
- **D)** Measure of an object's mass, unrelated to its motion

Acceleration, describing the rate of change of an object's velocity over time, occurs whenever an object's velocity changes in:

- **A)** Magnitude only, with direction change never counting as acceleration
- **B)** Direction only, with magnitude (speed) change never counting as acceleration
- **C)** Neither magnitude nor direction, by definition
- **D)** EITHER magnitude (speeding up or slowing down) OR direction (even at constant speed) - since velocity is a vector, any change in either its magnitude or its direction constitutes a change in velocity, and thus represents acceleration; this is why an object moving in a circular path at constant speed is still continuously accelerating (centripetal acceleration), due to its continuously changing direction

Newton's first law of motion (the law of inertia) states that an object will:

- **A)** Always eventually come to rest on its own, even with no external forces acting on it
- **B)** Remain at rest, or continue moving at a constant velocity in a straight line, UNLESS acted upon by a net external force - objects have an inherent property (inertia) resisting any change to their current state of motion, and inertia is directly proportional to an object's mass
- **C)** Spontaneously accelerate without any external force being applied
- **D)** Only obey this law while in outer space, with no application on Earth

Newton's second law of motion, expressed by the equation F = ma, describes the relationship between the net force acting on an object, its mass, and its resulting acceleration; this equation indicates that, for a constant applied net force, an object's acceleration is:

- **A)** Directly proportional to its mass (larger mass producing larger acceleration for the same force)
- **B)** Completely independent of and unrelated to its mass
- **C)** INVERSELY proportional to its mass (a = F/m) - for the same net applied force, a more massive object will experience proportionally LESS acceleration than a less massive object, reflecting the more massive object's greater inertia (resistance to a change in its motion)
- **D)** Always exactly equal to the net force applied, regardless of the object's mass

Newton's third law of motion states that for every action force one object exerts on a second object, there is:

- **A)** No corresponding reaction force at all
- **B)** A reaction force of equal magnitude acting in the SAME direction (not opposite)
- **C)** A reaction force of a completely different, unrelated magnitude
- **D)** A reaction force of EQUAL magnitude but OPPOSITE direction, exerted by the second object back onto the first object - these action-reaction force pairs always act on two DIFFERENT objects (never on the same single object), which is why they do not simply cancel each other out and prevent all motion, despite being equal and opposite

Weight, an object's gravitational force, differs from mass in that weight:

- **A)** Is a fundamental, unchanging property of matter that never varies for a given object, identical to mass
- **B)** Depends on the local gravitational field strength (g) acting on that object, and can therefore vary depending on location (e.g., an object's weight on the Moon is considerably less than its weight on Earth, due to the Moon's weaker gravitational field), while the object's MASS (a measure of the amount of matter present, and its inherent resistance to acceleration/inertia) remains constant regardless of location
- **C)** Is measured in units of kilograms, identical to mass
- **D)** Has no relationship whatsoever to gravitational force

Work, in the physics sense, is done on an object when:

- **A)** A force is applied to an object, regardless of whether the object actually moves any distance as a result
- **B)** An object moves any distance, regardless of whether any force is actually acting on it during that motion
- **C)** A force is applied to an object AND that object undergoes displacement (moves some distance) in at least partially the SAME direction as the applied force component - work is calculated as W = F x d x cos(θ), where θ is the angle between the force and displacement direction vectors, meaning a force applied exactly perpendicular to an object's actual displacement direction does zero work on that object
- **D)** An object's mass changes, regardless of any force or displacement

Kinetic energy, the energy an object possesses due to its motion, is calculated using the formula KE = (1/2)mv^2, indicating that kinetic energy scales:

- **A)** Linearly (directly proportionally) with an object's velocity
- **B)** With the SQUARE of an object's velocity - meaning that DOUBLING an object's velocity QUADRUPLES its kinetic energy (since 2^2 = 4), a nonlinear relationship with significant practical implications (e.g., in vehicle collision physics, where even modest speed increases substantially increase kinetic energy and thus potential collision severity)
- **C)** Inversely with an object's velocity
- **D)** With an object's mass alone, having no relationship whatsoever to velocity