Forces, Energy And Power

Question 1

Describe the principle of conservation of energy.

Answer 1

The principle of conservation of energy states that energy cannot be created or destroyed, but can be transferred from one form to another, keeping the total energy in a closed system constant.

Question 2

Define energy in the context of physics.

Answer 2

Energy is defined as the capacity to do work and comes in different forms such as gravitational potential energy, kinetic energy, internal energy, elastic potential energy, and electrical potential energy.

Question 3

How does gravitational potential energy change with height?

Answer 3

Gravitational potential energy increases as an object’s height above the ground increases, depending on the object’s position in a gravitational field and its mass.

Question 4

Explain kinetic energy and its dependence on mass and velocity.

Answer 4

Kinetic energy is the energy stored by an object when it is moving, and it is dependent on the object’s mass and velocity.

Question 5

What is internal energy?

Answer 5

Internal energy is equal to the sum of all the kinetic energies and potential energies of all the particles of an object.

Question 6

Describe elastic potential energy.

Answer 6

Elastic potential energy is the energy stored by an object when it is squashed or stretched.

Question 7

What factors influence electrical potential energy?

Answer 7

Electrical potential energy is dependent on a charged object’s position in an electric field.

Question 8

How is energy transferred when work is done?

Answer 8

Energy is transferred from one form to another when work is done, such as when kinetic energy is converted into elastic potential energy when an object is squashed.

Question 9

Explain how energy is emitted or absorbed in the form of electromagnetic radiation.

Answer 9

Energy is emitted or absorbed in the form of electromagnetic radiation when thermal/internal energy is transmitted, for example, by infrared radiation from a radiator.

Question 10

Describe the energy transformation that occurs when a ball is thrown into the air.

Answer 10

When a ball is thrown into the air, kinetic energy is converted into gravitational potential energy as it rises, and then back into kinetic energy as it falls.

Question 11

What happens to kinetic energy when a ball works against resistive forces?

Answer 11

When a ball works against resistive forces, such as air resistance, the initial kinetic energy given to the ball is not equal to the maximum gravitational potential energy when the ball stops in mid-air, as some energy is transferred to the environment as heat.

Question 12

Define work done in physics.

Answer 12

Work done (W) is defined as the force causing a motion multiplied by the distance travelled in the direction of the motion.

Question 13

What is the formula for calculating work done?

Answer 13

The formula for calculating work done is W = F s cos θ, where F is the force, s is the distance, and θ is the angle between the force and the direction of motion.

Question 14

Describe the relationship between work done and the change in volume of a gas at constant pressure.

Answer 14

Work done on a gas to change its volume at constant pressure can be calculated using the formula W = p ΔV, where p is the pressure and ΔV is the change in volume.

Question 15

How is efficiency calculated in a system?

Answer 15

Efficiency is calculated by dividing the useful power output by the total energy input, expressed as a percentage by multiplying the result by 100.

Question 16

Define kinetic energy and its formula.

Answer 16

Kinetic energy (E_k) is the energy of an object in motion, calculated using the formula E_k = 1/2 mv^2, where m is the mass and v is the velocity of the object.

Question 17

Explain why the efficiency of a system is never 100%.

Answer 17

The efficiency of a system is never 100% because energy is always lost due to various forms of friction, such as kinetic energy being converted to internal and sound energy.

Question 18

What factors contribute to energy loss in a system?

Answer 18

Energy loss in a system can occur due to friction, heat transfer, and the conversion of kinetic energy to internal and sound energy.

Question 19

How can you derive the equation for kinetic energy from Newton’s 2nd law?

Answer 19

The equation for kinetic energy can be derived by considering an object of mass m that accelerates uniformly from rest to velocity v, using the relationships between force, mass, acceleration, and distance.

Question 20

What does the variable ‘s’ represent in the context of work done?

Answer 20

In the context of work done, ‘s’ represents the distance travelled by the object.

Question 21

What is the significance of the angle θ in the context of work done?

Answer 21

The angle θ represents the angle between the direction of the force applied and the direction of motion, affecting the calculation of work done.

Question 22

How can efficiency be expressed as a percentage?

Answer 22

Efficiency can be expressed as a percentage by multiplying the ratio of useful power output to total energy input by 100.

Question 23

Describe the difference between gravitational potential energy and elastic potential energy.

Answer 23

Gravitational potential energy depends on an object’s position in a gravitational field and its mass, while elastic potential energy depends on an object’s elasticity or spring constant and its change in length.

Question 24

Explain the relationship between work done and gravitational potential energy.

Answer 24

If a force is applied to an object and it does positive work (increasing the object’s height), the gravitational potential energy of the object will increase. Conversely, if the height decreases, the gravitational potential energy will decrease.

Question 25

What factors influence the change in gravitational potential energy when a force is applied?

Answer 25

The change in gravitational potential energy is influenced by the magnitude of the force applied and the change in height (Δh) of the object.

Question 26

Define the equation for work done in relation to gravitational potential energy.

Answer 26

Work done (W) is the product of force and distance travelled, and for gravitational potential energy, it is equal to the weight of the object multiplied by the change in height: W = m * g * Δh.

Question 27

What is the principle of conservation of energy in the context of kinetic and gravitational potential energy?

Answer 27

The principle of conservation of energy states that the total energy (kinetic and gravitational potential) in a closed system remains constant, ignoring external factors like air resistance.

Question 28

What is the significance of ignoring air resistance in energy calculations for a pendulum?

Answer 28

Ignoring air resistance simplifies the calculations by assuming that all potential energy converts to kinetic energy without losses, allowing for straightforward application of conservation of energy principles.

Question 29

Define power in the context of energy transfer.

Answer 29

Power (P) is defined as the rate of energy transfer, which is the amount of energy transferred per unit time.

Question 30

Explain the relationship between work and power.

Answer 30

Work is a measure of energy transfer, and the rate of doing work is equal to the rate of energy transfer, which can be expressed as P = W/t.