NGSA Energy Practice Test Answer Key

Question 1

A roller coaster car is at the top of a hill. As it descends, which energy transformation primarily occurs?

Correct Answer: Potential energy to kinetic energy

Thought Process:
At the top of the hill, the roller coaster car has maximum gravitational potential energy due to its height. As it descends, its height decreases, and its speed increases. This means the stored potential energy is being converted into energy of motion, which is kinetic energy. The primary transformation is from potential energy to kinetic energy.

Question 2

Which of the following scenarios best demonstrates the conversion of chemical energy into light and thermal energy?

Correct Answer: A battery powering a flashlight.

Thought Process:

• A hydroelectric dam generating electricity: This is potential energy (water height) to kinetic energy (moving water) to mechanical energy (turbine) to electrical energy.
• A photovoltaic cell converting sunlight into electricity: This is radiant (light) energy to electrical energy.
• A battery powering a flashlight: A battery stores chemical energy. When activated, this chemical energy is converted into electrical energy, which then powers the bulb, producing light energy and thermal energy (heat).
• A person running a marathon: This involves chemical energy (from food) converting into mechanical energy (muscle movement) and thermal energy.
  Therefore, the flashlight best represents chemical to light and thermal energy.

Question 3

Explain the Law of Conservation of Energy and provide a real-world example of how it applies, even when energy appears to be 'lost'.

Thought Process:

• Law of Conservation of Energy: State the law clearly. Energy cannot be created or destroyed; it can only change forms or be transferred from one system to another. The total amount of energy in a closed system remains constant.
• Real-world example: Choose an example where energy transformation isn't 100% efficient in desired output. Common examples include: a car braking, a bouncing ball, or a light bulb.
• Explanation: When a car brakes, its kinetic energy (energy of motion) doesn't disappear. Instead, it's transformed into thermal energy (heat) due to friction between the brake pads and the wheels, and between the tires and the road. While the car's motion stops, the total energy of the system (car + brakes + surroundings) remains the same, just in different forms, predominantly heat that dissipates into the environment.
  
  
  
  
  
  
  
  
  
  
  

Question 4

A student pushes a box across a rough floor. Why does the box eventually stop, even if the student applied a consistent force initially?

Correct Answer: The mechanical energy is transformed into thermal energy due to friction.

Thought Process:
When the student pushes the box, they are doing work on it, giving it kinetic energy. However, the rough floor exerts a frictional force opposing the motion. This friction converts the box's kinetic energy into thermal energy (heat) due to the rubbing surfaces. This dissipation of energy as heat causes the box to slow down and eventually stop. Energy is conserved, but the kinetic energy is transformed into thermal energy.

Question 5

Which of the following is an example of nuclear energy being transformed into electrical energy?

Correct Answer: Fission in a nuclear power plant.

Thought Process:

• Sunlight hitting a solar panel: Radiant energy to electrical energy.
• Burning wood in a fireplace: Chemical energy to thermal and light energy.
• Fission in a nuclear power plant: Nuclear fission (splitting atoms) releases a vast amount of thermal energy, which is used to boil water, create steam, turn a turbine (mechanical energy), and then generate electricity (electrical energy).
• A wind turbine spinning: Kinetic energy (wind) to mechanical energy (turbine) to electrical energy.
  Therefore, nuclear power plants are the direct example of nuclear energy transforming into electrical energy.

Question 6

Describe two different forms of energy involved in ringing a doorbell and trace their transformations from the moment you press the button to the sound being heard.

Thought Process:

• Action: Pressing the doorbell button.
• Form 1: Mechanical Energy: The finger pressing the button applies mechanical force, doing work to move the button mechanism. This mechanical energy is transferred to the internal components.
• Transformation 1: Electrical Energy: Inside the doorbell, pressing the button completes an electrical circuit. This converts the mechanical action into electrical energy flowing through the wires.
• Transformation 2: Magnetic/Mechanical Energy: The electrical current typically activates an electromagnet, which then pulls a small hammer (more mechanical energy) to strike a bell or chime.
• Form 2: Sound Energy: The striking of the bell creates vibrations, which produce sound energy that travels through the air to your ears.
  (Optional: Some thermal energy is also produced due to resistance in the wires and friction in moving parts, demonstrating conservation.)
  
  
  
  
  
  
  
  
  
  
  

Question 7

A stretched rubber band stores what type of energy?

Correct Answer: Elastic potential energy

Thought Process:

• Kinetic energy: Energy of motion (the rubber band is stationary when stretched).
• Gravitational potential energy: Energy due to height (not primary for a rubber band).
• Chemical energy: Energy stored in chemical bonds (not the primary form for a stretched rubber band).
• Elastic potential energy: Energy stored in an object when it is stretched or compressed and will return to its original shape when released. This perfectly describes a stretched rubber band.

Question 8

In a closed system, if the total energy at the beginning is 100 Joules, and 20 Joules are transformed into thermal energy due to friction, what is the total amount of other forms of energy remaining?

Correct Answer: 100 Joules

Thought Process:
The Law of Conservation of Energy states that in a closed system, the total amount of energy remains constant. Even though 20 Joules were transformed into thermal energy due to friction, that thermal energy is still part of the total energy within the system. It hasn't been created or destroyed. Therefore, the total energy of the system is still 100 Joules, just distributed among different forms (80 Joules of the 'other' forms + 20 Joules of thermal energy = 100 Joules total). The question asks for the total amount of other forms of energy remaining, which is a bit tricky. If it means the sum of all forms excluding the thermal energy, then it would be 80 Joules (100 - 20). However, if it means the total energy of the system, which is what 'remaining' implies in a conservation context, it's 100 Joules. Given the context of the Law of Conservation, the total energy of the system remains 100 Joules. The wording is slightly ambiguous, but the fundamental principle is that total energy is conserved. For a multiple-choice question on NGSA, they would usually be clearer about