Modelling in Mechanics

Question 1

Model 1

Answer 1

A mathematical system which enables a problem to be solved

Question 2

Light 1

Answer 2

Has negligible mass

Question 3

Static 1

Answer 3

Not moving

Question 4

Rigid 1

Answer 4

Doesn’t bend

Question 5

Thin 1

Answer 5

Has negligible mass

Question 6

Light String 1

Answer 6

Has negligble mass and equal tension at both ends

Question 7

Particle 1, 2

Answer 7

Dimensions of the object are negligible

• mass of the object is concentrated at a single point
• rotational forces and air resistance can be ignored

Question 8

Rod 1, 3

Answer 8

All dimensions but one are negligible

• mass is concentrated along a line
• no thickness
• rigid

Question 9

Lamina 1, 1

Answer 9

Object with area but negligible thickness

• mass is distributed across a flat surface

Question 10

Uniform Body 1, 1

Answer 10

Mass is distributed evenly

• mass of the object is concentrated at a single point at the geometrical centre of the body (centre of mass)

Question 11

Light Object 1, 2

Answer 11

Mass of the object is small compared to other masses

• treat object as having zero mass
• tension the same at both ends of a light string

Question 12

Inextensible String 1, 1

Answer 12

A string that doesn’t stretch under load

• acceleration is the same in objects connected by a taut inextensible string

Question 13

Smooth Surface 1

Answer 13

• assume that there is no friction between the surface and any object on it

Question 14

Rough Surface 1

Answer 14

• objects in contact with the surface experience a frictional force if they are moving or are acted on by a force

Question 15

Wire 1, 1

Answer 15

Rigid thin length of material

• treated as one-dimensional

Question 16

Smooth and Light Pulley 1, 2

Answer 16

All pulleys you consider will be smooth and light

• pulley has no mass
• tension is the same on either side of the bead

Question 17

Bead 1, 2

Answer 17

Particle with a hole in it for threading on a wire or string

• moves freely along a wire or string
• tension is the same on either side of the bead

Question 18

Peg 1, 2

Answer 18

A support from which a body can be suspended or rested

• dimensionless and fixed
• can be rough or smooth as specified in question

Question 19

Air Resistance 1, 1

Answer 19

Resistance experienced as an object moves through the air

• usually modelled as being negligible

Question 20

Gravity 1, 3

Answer 20

Force of attraction between all objects. Acceleration due to gravity is denoted by g

• assume that all objects with mass are attracted towards the Earth
• Earth’s gravity is uniform and acts vertically downwards
• g is constant and is taken as 9.8m/s2