AP Physics 1:: Energy

What is WORK, in the specific PHYSICS sense of the term, and what TWO quantities are multiplied together to calculate the work done by a CONSTANT force acting in the SAME direction as an object's displacement?

- **A)** Work is the TRANSFER of energy via a force acting through a displacement; W = F*d (force multiplied by displacement), when the force is parallel to the displacement direction
- **B)** Work is calculated by DIVIDING force by displacement (W = F/d), rather than multiplying them together
- **C)** Work refers only to the TIME an object spends under the influence of a force, with no relationship to displacement
- **D)** This concept has no actual mathematical relationship between force and displacement in calculating work

Why does a force do ZERO WORK on an object if that force acts PERPENDICULAR to the object's displacement (e.g., the normal force on an object sliding along a horizontal surface)?

- **A)** This concept has no actual relationship to why a perpendicular force contributes no work to an object's displacement
- **B)** Work depends on the COMPONENT of force that is PARALLEL to displacement; a force acting entirely PERPENDICULAR to displacement has ZERO parallel component, and therefore does zero work, regardless of the force's magnitude
- **C)** A perpendicular force always does the MAXIMUM possible amount of work, rather than zero work
- **D)** Perpendicular forces can never actually act on a moving object, making this scenario physically impossible

For a force acting at an ANGLE to an object's displacement (neither fully parallel nor fully perpendicular), what is the COMPLETE formula for WORK, incorporating this angle?

- **A)** W = F*d*cos(theta), where 'theta' is the angle between the force vector and the displacement vector -- this formula correctly reduces to W=Fd when theta=0 (parallel) and W=0 when theta=90 degrees (perpendicular)
- **B)** The complete work formula requires ADDING (rather than multiplying) force, displacement, and the cosine of their angle together
- **C)** Work is calculated using SINE (rather than cosine) of the angle between force and displacement, contradicting the standard work formula
- **D)** This formula has no actual relationship to incorporating the angle between a force and an object's displacement when calculating work

What is KINETIC ENERGY, and what is the mathematical FORMULA relating an object's kinetic energy to its MASS and SPEED?

- **A)** This concept has no actual mathematical relationship between an object's kinetic energy, its mass, and its speed
- **B)** Kinetic energy is INVERSELY proportional to the square of an object's speed, rather than directly proportional to it
- **C)** The energy an object possesses due to its MOTION; KE = (1/2)*m*v^2 -- kinetic energy is proportional to mass, and proportional to the SQUARE of speed
- **D)** Kinetic energy is calculated as KE = m*v (mass times speed, without squaring or the 1/2 factor), rather than the correct (1/2)mv^2 formula

According to KE = (1/2)mv^2, if an object's SPEED is DOUBLED while its MASS stays the SAME, how does its KINETIC ENERGY change?

- **A)** Kinetic energy simply DOUBLES, treating the relationship as if it were linear rather than dependent on the square of speed
- **B)** Speed has no actual relationship to an object's kinetic energy for a given, constant mass
- **C)** Kinetic energy is CUT IN HALF when speed doubles, the reverse of the actual relationship between speed and kinetic energy
- **D)** Kinetic energy QUADRUPLES (increases by a factor of 4), since KE depends on the SQUARE of speed

What is GRAVITATIONAL POTENTIAL ENERGY, and what is the mathematical FORMULA for an object's gravitational potential energy NEAR Earth's surface, in terms of its mass, the local gravitational acceleration, and its HEIGHT above a chosen reference point?

- **A)** Gravitational potential energy DECREASES as an object's height above the reference point increases, the reverse of the actual relationship
- **B)** Gravitational potential energy is calculated as PE = m*g/h (mass times gravitational acceleration divided by height), rather than mass times g times height
- **C)** This concept has no actual mathematical relationship between an object's gravitational potential energy, its mass, gravitational acceleration, and height
- **D)** Energy an object possesses due to its POSITION within a gravitational field; PE_gravity = m*g*h (mass times gravitational acceleration times height above a chosen reference point)

Why is it necessary to choose a SPECIFIC REFERENCE POINT (sometimes called a 'zero height' level) before calculating an object's GRAVITATIONAL POTENTIAL ENERGY using PE=mgh?

- **A)** Gravitational potential energy has an absolute, fixed value that does NOT depend on any chosen reference point, making such a reference point completely unnecessary
- **B)** The reference point for gravitational potential energy must always be chosen as the CENTER of the Earth, with no other reference point ever being valid
- **C)** Gravitational potential energy is defined RELATIVE to a chosen reference point -- since only CHANGES in potential energy actually matter for solving most physics problems, the reference point can be chosen ARBITRARILY (for convenience), as long as it's used CONSISTENTLY throughout a given problem
- **D)** This concept has no actual relationship to why a reference point must be chosen before calculating gravitational potential energy

What is ELASTIC POTENTIAL ENERGY, and what is the mathematical FORMULA for the elastic potential energy stored in a COMPRESSED or STRETCHED IDEAL SPRING, in terms of the spring constant and displacement from equilibrium?

- **A)** Energy stored in a DEFORMED elastic object (like a compressed or stretched spring); PE_spring = (1/2)*k*x^2 (one-half times the spring constant times the SQUARE of the displacement from the spring's natural, equilibrium length)
- **B)** Elastic potential energy DECREASES as a spring's displacement from equilibrium increases, the reverse of the actual relationship
- **C)** Elastic potential energy is calculated as PE_spring = k*x (spring constant times displacement, without squaring or the 1/2 factor), rather than the correct (1/2)kx^2 formula
- **D)** This concept has no actual mathematical relationship between elastic potential energy, the spring constant, and the displacement from equilibrium