Question

1. a roller coaster climbs a hill using a motorized chain. at the top, the chain releases the car. which statement best explains the dominant energy transformation as the car begins its descent? thermal energy → nuclear energy b. kinetic energy → gravitational potential energy c. gravitational potential energy → kinetic energy d. chemical energy → electrical energy 2. a scientist designs a battery - powered drone and wants to maximize flight time. which modification would most effectively reduce unwanted energy transformations? a. increase the battery mass to store more chemical energy b. use motors that produce less heat during operation c. increase blade speed to raise kinetic energy output d. add more led lights for visibility 3. when a car brakes, the brake pads heat up significantly. which conclusion best explains the energy transformation occurring? a. chemical energy is stored in the brake pads. b. the car’s kinetic energy is converted primarily to thermal energy. c. thermal energy is converted into electrical energy. d. the car’s potential energy increases. 4. a wind turbine produces electricity more efficiently on colder days. why might this be the case? a. the blades store more chemical energy. b. colder air is denser, increasing kinetic energy transfer from the wind. c. cold temperatures increase gravitational potential energy. d. the turbine converts thermal energy into electrical energy. 5. a student claims: \if no external work is done on a system, the total energy stays the same.\ in which situation would this claim not hold true? a. a satellite orbiting earth b. a pendulum swinging without air resistance c. a block sliding on a rough surface d. a planet orbiting the sun

Explanation:

1. At the top of the hill, the roller - coaster car has gravitational potential energy. As it descends, this potential energy is converted into kinetic energy (energy of motion).
2. Unwanted energy transformations often result in energy loss (e.g., as heat). Using motors that produce less heat during operation reduces such unwanted losses, which helps in maximizing flight time (as more energy is used for the intended purpose of flight).
3. When a car brakes, its kinetic energy (due to its motion) is dissipated. The brake pads heating up shows that this kinetic energy is being converted into thermal energy (heat).
4. Colder air is denser. Denser air has more mass per unit volume. When wind (which has kinetic energy) hits the wind - turbine blades, more kinetic energy is transferred (since the air has more mass, and kinetic energy \(K = \frac{1}{2}mv^{2}\), where \(m\) is mass and \(v\) is velocity) when the air is denser.
5. The law of conservation of energy (total energy of a closed system remains constant if no external work is done) holds for systems with no non - conservative forces (like friction). A block sliding on a rough surface experiences friction (a non - conservative force). Friction causes energy (in the form of kinetic energy of the block) to be converted into thermal energy (heat due to friction), so the total mechanical energy of the block (kinetic + potential) is not conserved.

Answer:

1. C. Gravitational potential energy → kinetic energy
2. B. Use motors that produce less heat during operation
3. B. The car’s kinetic energy is converted primarily to thermal energy.
4. B. Colder air is denser, increasing kinetic energy transfer from the wind.
5. C. A block sliding on a rough surface