Topic 02: Mechanics

Question 1

Centre of mass

Answer 1

The average point of all parts of an object weighted according to their mass. It is the point through which the total mass of the object is said to act

Question 2

Conservation of energy

Answer 2

In a closed system with no external forces, the energy of the system before an event is equal to the energy of the system after the event. The energy does not need to be in the same form after the event as it was before the event

Question 3

Conservation of momentum

Answer 3

In a closed system with no external forces, the momentum of the system before an event is equal to the momentum of the system after the event

Question 4

Drag

Answer 4

The resistance against the motion of an object through a fluid. It is usually proportional to the speed of the object

Question 5

Efficiency

Answer 5

The useful output (e.g. power, energy) of a system divided by the total output

Question 6

Elastic collision

Answer 6

When the kinetic energy of a system before an event is equal to the kinetic energy of the system after the event

Question 7

Equilibrium

Answer 7

An object is at equilibrium when the moments on it about a point are balanced and the resultant force on the object is zero

Question 8

Force

Answer 8

The rate of change of momentum of an object. The product of the object’s mass with its acceleration

Question 9

Friction

Answer 9

The resistance against the motion of an object. This could be caused by the air passing over the object, or by the contact of the object with the surface it is moving on

Question 10

Gravitational potential energy

Answer 10

The energy gained by an object when it is raised by a height in a gravitational field

Question 11

Impulse

Answer 11

The change of momentum of an object when a force acts on it. Equal to the area underneath a force-time graph

Question 12

Inelastic collision

Answer 12

When the kinetic energy of a system before an event is not equal to the kinetic energy of the system after the event. The kinetic energy has been transferred to other forms

Question 13

Kinetic energy

Answer 13

The energy an object has due to its motion. It is the amount of energy that would be transferred from the object when it decelerates to rest

Question 14

Lift

Answer 14

A force acting perpendicular to the flow of air or liquid around an object, typically upwards and against the force of gravity

Question 15

Moment

Answer 15

The product of a force and the perpendicular distance from the line of action to the pivot about which the force is acting

Question 16

Momentum

Answer 16

The product of an object’s mass and its velocity

Question 17

Newton’s first law

Answer 17

An object at a constant velocity will remain at a constant velocity unless acted on by a resultant force. (If this constant velocity is zero, the object is at rest)

Question 18

Newton’s second law

Answer 18

If an object is acted upon by a resultant force, it will accelerate. The acceleration is inversely proportional to the mass of the object and directly proportional to the force acting upon it

Question 19

Newton’s third law

Answer 19

Every action has an equal and opposite reaction. If an object A exerts a force on object B, object B will exert a force of equal magnitude but of opposite direction on object A

Question 20

Power

Answer 20

The work done by a system divided by the time taken for that work to be done

Question 21

Resultant force

Answer 21

The sum of all forces on an object

Question 22

Scalar

Answer 22

A quantity with only magnitude and no direction (e.g. mass, energy, length)

Question 23

Terminal velocity

Answer 23

The maximum velocity an object can achieve. It is the point at which the frictional force and driving forces are balanced and so no acceleration occurs and the resultant force on the object is 0 N

Question 24

Vector

Answer 24

A quantity with magnitude and direction (e.g. velocity, acceleration, force)

Question 25

Weight

Answer 25

The force of gravity on an object, the product of the object’s mass, and the acceleration due to gravity

Question 26

Work done

Answer 26

A force applied over a distance, it is the energy transferred in that direction