Modelling assumptions

Question 1

What 3 assumptions are made when the object is modelled as a particle?

Answer 1

1. the mass of the object is concentrated at a single point
2. rotational forces can be ignored
3. air resistance can be ignored

Question 2

What 3 assumptions can be made when an object is modelled as a rod?

Answer 2

1. the mass is concentrated along a line
2. no thickness
3. rigid

Question 3

What is a lamina?

Answer 3

An object with an area but negligible thickness (like paper)

Question 4

What assumption can be made if an object is modelled as a lamina?

Answer 4

mass is distributed across a flat surface

Question 5

What assumption can be made with a uniform body?

Answer 5

mass is concentrated at the centre of mass

Question 6

What 2 assumptions can be made when an object is light?

Answer 6

1. treat object as having zero mass
2. tension is the same at both ends of a light string

Question 7

What assumption can be made with an inextensible string?

Answer 7

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

Question 8

What assumption can be made when a surface is smooth?

Answer 8

no friction between surface and any object on it

Question 9

What assumption can be made when a surface is rough?

Answer 9

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

Question 10

What assumption can be made with a wire?

Answer 10

it has one-dimension

Question 11

What 2 assumptions can be made with a smooth and light pulley?

Answer 11

1. pulley has no mass
2. tension is the same on either side of the pulley

Question 12

What 2 assumptions can be made with a bead?

Answer 12

1. moves freely along wire or string
2. tension is the same either side of the bead

Question 13

What 2 assumptions can be made with a peg?

Answer 13

1. dimensionless
2. fixed

Question 14

Air resistance is usually modelled as being __________.

Answer 14

negligible

Question 15

What 3 assumptions can be made with gravity?

Answer 15

1. all objects with mass are attracted towards the Earth
2. Earth’s gravity is uniform and acts vertically downwards
3. g is constant and is taken as 9.8 m/s2 (unless otherwise stated in the question)

Question 16

What does it mean when an object is modelled as a particle? (1 mark)

Answer 16

The dimensions of the object are negligible.

Question 17

What does it mean when an object is modelled as a rod? (1 mark)

Answer 17

All dimensions but one are negligible, like pole or beam

Question 18

What does it mean when an object is modelled as a laminate? (1 mark)

Answer 18

The object has an area but negligible thickness, like paper.

Question 19

What is meant by a ‘uniform body’? (1 mark)

Answer 19

The mass is distributed evenly.

Question 20

What is meant by a ‘light object’? (1 mark)

Answer 20

The mass of the object is small in comparison with other masses, like a string/pulley.

Question 21

What is meant by a ‘wire’? (1 mark)

Answer 21

A rigid thin length of metal.

Question 22

What is the normal reaction? (2 marks)

Answer 22

The upward force that acts perpendicular to a surface when an object is in contact with the surface.