Chapter 8 Modelling in Mechanics (AS)

Question 1

What are the modelling assumptions of a particle?

Answer 1

• Dimensions of the object are negligible
• its mass is concentrated at a single point
• Air resistance and rotational forces can be ignored

Question 2

What are the modelling assumptions of a Rod?

Answer 2

• An object with 1 dimension (length).
• Its mass is distributed along a straight line
• it has no thickness and is rigid (does not bend or buckle)

Question 3

What are the modelling assumptions of a lamina?

Answer 3

• An object with 2 dimensions (width and length).
• Its mass is evenly distributed across a flat surface

Question 4

What are the modelling assumptions of uniform body?

Answer 4

• Its mass is evenly distributed.
• Mass of the object is concentrated at a single point at the geometrical centre of the body (the centre of mass)

Question 5

What are the modelling assumptions of a light object?

Answer 5

• Its mass is very small and the mass is therefore treated as 0.
• Tension is the same at both ends of a light string

Question 6

What are the modelling assumptions of an inextensible string?

Answer 6

• A string that does not stretch under load.
• Acceleration is constant in objects connected by a taut inextensible string

Question 7

What are the modelling assumptions of a smooth surface?

Answer 7

It is assumed that there is no friction between the surface and the object on it

Question 8

What are the modelling assumptions of a rough surface?

Answer 8

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

Question 9

What are the modelling assumptions of a wire?

Answer 9

A rigid thin length of metal which is treated as 1 dimensional

Question 10

What are the modelling assumptions of a bead?

Answer 10

• Particle with a hole in it for threading on a wire or string.
• It moves freely along the wire or string and tension is the same on either side of the bead

Question 11

What are the modelling assumptions of a peg?

Answer 11

• A support from which a body can be suspended or rested.
• It is dimensionless and fixed

Question 12

What are the modelling assumptions of air resistance?

Answer 12

• frictional resistance experienced as an object moves through the air

Question 13

What are the modelling assumptions of gravity?

Answer 13

• The force of attraction to the earth, measured at 9.8 ms⁻².
• It is uniform and acts vertically downwards. all objects with mass are attracted towards the earth

Question 14

Mass

Answer 14

kilogram (kg)

Question 15

Length/Displacement

Answer 15

metre (m)

Question 16

Time

Answer 16

Seconds (s)

Question 17

Speed/Velocity

Answer 17

metres per second (ms^-1)

Question 18

Acceleration

Answer 18

metres per second per second (ms^-2)

Question 19

Force/Weight

Answer 19

Newton (N)

Question 20

A scalar quantity has…

Answer 20

only magnitude

Question 21

A vector quantity..

Answer 21

has direction and magnitude

Question 22

Scalar -> Vector

Distance =

Speed =

Answer 22

Displacement

Velocity