Work, Energy & Power

Question 1

Definition of work done

Answer 1

The work done by a force on a body is the product of that force and the displacement of the body in the direction of the force.

Question 2

Formula of work done

Answer 2

W = F s cos θ

Question 3

What is the unit of work and is it scalar or vector?

Answer 3

Joule(J)
Scalar

Question 4

What is one joule?

Answer 4

A joule is the work done by a force of 1 newton when its point of application moves through a displacement of 1 metre in the direction of the force.

Question 5

Definition of energy and work

Answer 5

Energy is the ability to do work.
Work is a process in which energy is transferred from one object to another through the action of a force on an object.

Question 6

How do you find work done from F-s graph?

Answer 6

Area under F-s graph

Question 7

How do you find work done by a gas at constant external pressure?

Answer 7

W = p(Vf - Vi)

Question 8

Definition of kinetic energy

Answer 8

Kinetic energy is a type of energy which a body possesses by virtue of its motion.

Question 9

What is the work-energy theorem?

Answer 9

The work done on a rigid body by the resultant force is always equal to the change in the kinetic energy of the body.

Question 10

Definition of gravitational potential energy

Answer 10

Gravitational potential energy is the energy possessed by a mass by virtue of its position in a gravitational field.

Question 11

Definition of electric potential energy

Answer 11

Elastic potential energy is the energy possessed by an electric charge by virtue of its position in an electric field produced by other electric charges.

Question 12

Definition of elastic potential energy

Answer 12

The energy of a system of atoms by virtue of their positions where the particles experience short-range interatomic attractive or repulsive forces.

Question 13

How do you find elastic potential energy from a force-extension graph?

Answer 13

Area under graph

Question 14

Formula for elastic potential energy

Answer 14

W = 1.2 kx^2(if Hooke’s law is being obeyed)

Question 15

Definition of potential energy

Answer 15

Potential energy is the energy stored in an object due to its position, shape or state.

Question 16

What is the relationship between force and potential energy?

Answer 16

F = -dU/dr
F is force and U is potential energy

Question 16

Definition of dissipative forces

Answer 16

Dissipative forces are forces whereby energy is lost from a system where motion takes place.

Question 17

Examples of dissipative forces

Answer 17

Kinetic frictional forces and viscous forces

Question 18

Definition of Principle of Conservation of Energy

Answer 18

The principle of conservation of energy states that the total energy of an isolated system is constant. Energy cannot be created or destroyed, but can be transferred from one form to another.

Question 18

Formula for Principle of Conservation of Energy

Answer 18

KE initial + PE initial + E supplied = KE final + PE final + E lost
Loss in KE = Gain in PE

Question 19

Definition of power

Answer 19

Power is defined as the rate of work done or energy transfer.

Question 20

Formula of power

Answer 20

P = dW/dt, P = Fv
P = W/t (if work done is constant)

Question 21

Unit of power

Answer 21

Watt(W) or joule per second( J/s)

Question 22

Definition of efficiency

Answer 22

It is the rate of useful energy output to the total energy input