Modelling assumptions

Question 1

Define particle

Answer 1

dimensions of the object are negligible

Question 2

Particle modelling assumptions

Answer 2

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

Question 3

Define rod

Answer 3

one dimension is negligible, like a pole or beam

Question 4

Rod modelling assumptions

Answer 4

• mass is concentrated along a line
• no thickness
• rigid –> does not bend or buckle

Question 5

Define lamina

Answer 5

object with are but negligible thickness, like a sheet of paper

Question 6

Lamina modelling assumptions

Answer 6

• mass is distributed across a flat surface

Question 7

Define uniform body

Answer 7

mass is distributed evenly

Question 8

Uniform body modelling assumptions

Answer 8

• mass of the object is concentration at a single point at the geometrical Centre of the body –> the centre of mass

Question 9

Define light object

Answer 9

mass of the object is small compared to other masses, like a string or a pulley

Question 10

Light object modelling assumptions

Answer 10

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

Question 11

Define inextensible string

Answer 11

a string that does not stretch under a load

Question 12

Inextensible string modelling assumptions

Answer 12

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

Question 13

Smooth surface modelling assumptions

Answer 13

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

Question 14

Define rough surface

Answer 14

if a surface is not smooth it is rough

Question 15

Rough surface modelling assumptions

Answer 15

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

Question 16

Define wire

Answer 16

rigid thin length of metal

Question 17

Wire modelling assumptions

Answer 17

• treated at one dimensional

Question 18

Define smooth and light pulley

Answer 18

all pulleys you consider will be smooth and light

Question 19

Smooth and light pulley modelling assumption

Answer 19

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

Question 20

Define bead

Answer 20

particle wit a hole in it for threading on a wire or string

Question 21

Bead modelling assumptions

Answer 21

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

Question 22

Define peg

Answer 22

a support from which a body can be suspended or rested

Question 23

Peg modelling assumptions

Answer 23

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

Question 24

Define air resistance

Answer 24

resistance experienced as an object moves through the air

Question 25

Air resistance modelling assumptions

Answer 25

- usually modelled as being negligible

Question 26

Define gravity

Answer 26

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

Question 27

What does g equal?

Answer 27

9.8 m/s2

Question 28

Gravity modelling assumptions

Answer 28

- assume that all objects with mass are attracted towards the earth - earths gravity is uniform and acts vertically downwards - g is constant and is taken as 9.8m/s2, unless otherwise stated in the question