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:

($W_f=-\mu_k N d$, where $\mu_k$ is the coefficient of kinetic friction, $N$ is the normal force, and $d$ is the distance) causes the mechanical energy (sum of kinetic and potential energy) of the block - surface system to decrease. The energy is lost as thermal energy (due to the heat generated by friction).

Answer:

C. A block sliding on a rough surface