Energy Unleashed: NGSA Style Test Answer Key

Question 1

Correct Answer: A) Chemical energy from the student is converted to kinetic energy of the box, with some energy lost as heat due to friction.

Thought Process:

• The student's body contains chemical energy from food. When the student pushes the box, this chemical energy is converted into the mechanical energy of pushing.
• This mechanical energy is then transferred to the box, causing it to move, thus gaining kinetic energy.
• Friction between the box and the floor, and air resistance, cause some of the kinetic energy to be converted into thermal energy (heat and sound), which is dissipated to the surroundings.
• Options B, C, and D contain inaccuracies in the initial energy source or the primary transformations.

Question 2

Correct Answer: A) A car slowing down as it drives up a hill.

Thought Process:

• Kinetic energy is the energy of motion, and gravitational potential energy is energy stored due to an object's position in a gravitational field.
• When a car drives up a hill, its height increases, meaning its gravitational potential energy increases. If it is also slowing down, its kinetic energy is decreasing. This indicates a conversion from kinetic energy to gravitational potential energy.
• B) A pendulum at the bottom of its swing has maximum kinetic energy and minimum potential energy.
• C) A ball falling from a tall building converts gravitational potential energy to kinetic energy.
• D) A spring compressing converts kinetic energy (of the weight) or potential energy (of the pushing force) into elastic potential energy of the spring.

Question 3

Prompt: A roller coaster car is at the top of a loop. Describe the energy transformations that occur as the car goes down the loop and then up the next hill. Explain how the principle of conservation of energy applies, considering any energy losses due to friction or air resistance.

Detailed Answer:

1. Top of the Loop: At the very top of the loop, the roller coaster car possesses maximum Gravitational Potential Energy relative to the lowest point of the track. Its Kinetic Energy is at a minimum (though not zero, as it must maintain some speed to complete the loop).

2. Going Down the Loop: As the car descends the loop, its height decreases, causing its Gravitational Potential Energy to be converted into Kinetic Energy. The car speeds up significantly, reaching its maximum kinetic energy (and minimum potential energy) at the bottom of the loop.

3. Climbing the Next Hill: As the car ascends the next hill, its Kinetic Energy is converted back into Gravitational Potential Energy. The car slows down as it gains height.

4. Conservation of Energy with Losses: The principle of Conservation of Energy states that energy cannot be created or destroyed, only transformed from one form to another. In an ideal system without friction or air resistance, the total mechanical energy (sum of kinetic and potential energy) would remain constant. However, in a real roller coaster, there are energy losses:

   • Friction: Between the wheels and the track, and within the moving parts, generates thermal energy (heat).
   • Air Resistance: As the car moves through the air, it does work against the air, converting some Kinetic Energy into thermal energy and sound energy.
   • Therefore, the total mechanical energy of the roller coaster car decreases over time. This lost mechanical energy is transformed into other forms, primarily thermal energy, and is dissipated into the environment. The total energy of the car and its surroundings (including the heat generated) remains conserved.

Question 4

Correct Answer: B) Gravitational Potential Energy → Kinetic Energy → Mechanical Energy → Electrical Energy

Thought Process:

• Gravitational Potential Energy: Water stored behind a dam at a height has gravitational potential energy.
• Kinetic Energy: When the water is released and flows downwards, its potential energy is converted into kinetic energy.
• Mechanical Energy: This kinetic energy of the water turns the turbines, which is a form of mechanical energy (rotational kinetic energy).
• Electrical Energy: The turbines are connected to generators, which convert the mechanical energy into electrical energy through electromagnetic induction.

Question 5

Prompt: Imagine you are designing a new type of renewable energy system for a remote island. Propose a system that utilizes at least two different forms of energy available on the island (e.g., solar, wind, ocean currents, geothermal). Explain how these energy forms would be captured, converted, and stored to provide a reliable power supply to the community.

Detailed Answer (Example Proposal - student answers may vary based on chosen sources):

Proposed System: Hybrid Solar-Wind-Battery System

Energy Sources Utilized:

1. Solar Energy: Abundant sunlight during the day.
2. Wind Energy: Consistent winds, especially along the coast or elevated areas.

Capture and Conversion:

1. Solar Energy:

   • Capture: Photovoltaic (PV) panels would be installed on rooftops and in open, sunny areas. These panels contain semiconductor materials that absorb sunlight.
   • Conversion: When sunlight strikes the PV panels, the photons excite electrons in the semiconductor material, generating an electric current. This process converts solar energy directly into direct current (DC) electrical energy. Inverters would then convert this DC electricity into alternating current (AC) for use by the island community.

2. Wind Energy:

   • Capture: Wind turbines would be strategically placed in locations with consistent high wind speeds (e.g., coastal areas or higher elevations). The blades of the turbines are designed to capture the kinetic energy of the wind.
   • Conversion: As wind pushes the turbine blades, they rotate. This rotational Kinetic Energy is transferred through a gearbox to a generator. The generator then converts this mechanical energy into electrical energy (AC electricity).

Energy Storage:

• Battery Storage: A large-scale battery energy storage system (BESS), such as lithium-ion batteries, would be integrated into the grid. During periods of high solar and/or wind generation and low demand, excess electricity would charge the batteries. When solar and wind generation are low (e.g., at night, during cloudy days, or calm periods) but demand is high, the stored energy in the batteries would be discharged to supply the community.

Reliable Power Supply:

• This hybrid system offers enhanced reliability compared to relying on a single renewable source. When there's no sun, there might be wind, and vice-versa. The battery storage acts as a buffer, ensuring a continuous supply even when both sources are intermittent.
• An intelligent energy management system would monitor generation, consumption, and battery levels to optimize the flow of electricity, prioritizing direct use of renewable energy and charging/discharging batteries as needed.

Potential Advantages:

• Reduced Carbon Footprint: Significantly lowers reliance on fossil fuels, reducing greenhouse gas emissions.
• Energy Independence: The island becomes less dependent on imported fuels, leading to greater energy security and stable costs.
• Cost Savings: Over the long term, operating costs are lower than fossil fuel generators.
• Scalability: The system can be expanded by adding more solar panels, wind turbines, or battery storage as demand grows.

Potential Disadvantages:

• Initial Investment Cost: Installation of solar panels, wind turbines, and a large battery system can be expensive.
• Intermittency: While combined, solar and wind are still intermittent. However, battery storage mitigates this significantly.
• Space Requirements: Wind turbines and large solar farms require considerable land area.
• Environmental Impact: While generally low, wind turbines can affect local wildlife (birds/bats) and visual aesthetics. Battery disposal needs to be managed responsibly.

Question 6

Correct Answer: B) In any energy transformation, some useful energy is always lost, primarily as heat.

Thought Process:

• This statement directly reflects the Second Law of Thermodynamics, often phrased in terms of entropy. It means that while the total energy in a closed system is conserved (First Law), the quality or usefulness of that energy tends to decrease during transformations. Some energy is always converted into a less usable form, most commonly thermal energy (heat) that disperses into the environment.
• A) Is incorrect; energy is conserved and cannot be created or destroyed (First Law of Thermodynamics), even in nuclear reactions (mass-energy equivalence, E=mc²).
• C) Is incorrect; the total amount of useful energy does not remain constant; it decreases due to the second law of thermodynamics. The total energy remains constant.
• D) Is a practical implication of energy efficiency but not a fundamental statement of the principle of energy conservation in physics.