Physics Energy and Momentum Quiz

Two particles in an isolated system collide elastically. Given their initial combined momentum of 37 kg•m/s, explain why the final combined momentum remains unchanged, and select the correct value.

• 5 kg•m/s

• 32 kg•m/s

• 37 kg•m/s

• 42 kg•m/s

Answer explanation

In an isolated system, momentum is conserved. The initial combined momentum of 37 kg•m/s remains unchanged after the elastic collision, leading to a final combined momentum of 37 kg•m/s.

Imagine designing a system that stores energy based on an object's height above the Earth. Which type of energy would you be primarily utilizing, and why?

• Elastic potential energy

• Kinetic energy

• Gravitational potential energy

• Mechanical energy

Answer explanation

The system primarily utilizes gravitational potential energy, as this type of energy depends on an object's height above the Earth. The higher the object, the more gravitational potential energy it possesses.

A motorcycle accelerates downhill. Analyze the energy transformation occurring midway down the hill, and determine the types of energy present.

• Entirely kinetic energy

• Entirely potential energy

• Entirely gravitational potential energy

• Both kinetic and potential energy

Answer explanation

Midway down the hill, the motorcycle has both kinetic energy from its motion and gravitational potential energy due to its height. As it accelerates downhill, potential energy converts to kinetic energy, making both types present.

Apply the given energy transformation sequence (chemical → heat → mechanical) to identify the scenario that best illustrates this process.

• A turbine spins.

• A headlight is on.

• Gasoline burns to run a jeepney.

• Electric current powers a flat iron.

Answer explanation

The scenario 'Gasoline burns to run a jeepney' illustrates the energy transformation sequence: chemical energy in gasoline is converted to heat energy during combustion, which then produces mechanical energy to power the vehicle.

Evaluate the following situations and determine which one demonstrates a decrease in gravitational potential energy, justifying your choice.

• A car ascends a steep parking ramp.

• Water is forced upward through a pipe.

• A puppy jumps down from a chair.

• A boy stretches a rubber band horizontally.

Answer explanation

A puppy jumping down from a chair demonstrates a decrease in gravitational potential energy because it moves from a higher position to a lower one, losing energy in the process.

A stone falls from a fence. Compare and contrast the stone's kinetic energy just before impact with its initial potential energy on the fence, explaining the relationship.

• KE is equal to PE.

• KE is less than PE.

• KE is greater than PE.

• KE is twice as much as PE.

Answer explanation

As the stone falls, its potential energy (PE) converts to kinetic energy (KE). Just before impact, all the initial PE is transformed into KE, making them equal. Thus, KE is equal to PE.

Calculate the gravitational potential energy of a 50 kg person at an altitude of 25 meters, showing your work.

• 12,150 J

• 12,250 J

• 12,350 J

• 12,250 J (corrected from the original list)

Answer explanation

Gravitational potential energy (GPE) is calculated using the formula GPE = mgh, where m = 50 kg, g = 9.8 m/s², and h = 25 m. Thus, GPE = 50 * 9.8 * 25 = 12,250 J. The correct answer is 12,250 J.

Determine the mass of an object with a kinetic energy of 243 J moving at 9 m/s, using the appropriate formula.

• 2 kg

• 4 kg

• 6 kg

• 8 kg

Answer explanation

To find mass, use the formula KE = 0.5 * m * v^2. Rearranging gives m = 2 * KE / v^2. Plugging in KE = 243 J and v = 9 m/s, we get m = 2 * 243 / (9^2) = 6 kg. Thus, the correct answer is 6 kg.

Identify the scientific field that focuses on the relationship between heat and its conversion into mechanical energy, and explain its significance.

• Conservation of energy

• Convection

• Radiation

• Thermodynamics

Answer explanation

Thermodynamics is the scientific field that studies the relationship between heat and mechanical energy conversion. It is significant because it underpins many engineering applications, including engines and refrigeration, influencing energy efficiency and technology.

Explain the primary method of heat transfer when cooking popcorn, and justify your choice.

• Through conduction

• Through convection

• Through radiation

• All of the options

Answer explanation

The primary method of heat transfer when cooking popcorn is through convection. As the kernels heat up, the surrounding air circulates, transferring heat evenly, which is essential for popping the kernels effectively.