Modelling in mechanics C8

Question 1

Define a particle, state its modelling assumption. (3)

Answer 1

⇒ Particle: Dimensions of the object are negligible (1)
⇒ Mass of the object is concentrated at a single point (1)
⇒ Rotational forces and air resistance can be ignored (1)

Question 2

Define what a light object is, state its assumptions. (3)

Answer 2

⇒ Light object: The mass of the object is small compared to the other masses (1)
⇒ Treat object as having zero mass (1)
⇒For a light string the tension is the same at both ends of a string

Question 3

Define what an Inextensible string is; state its assumption. (2)

Answer 3

⇒ Inextensible string: A string that does not stretch under load (1)
⇒ Acceleration is the same in the objects connected by a taut inextensible string (1)

Question 4

State the assumption of a smooth surface (1)

Answer 4

⇒ Smooth surface: Assume there is no friction between the surface and any object on it (1)

Question 5

Define what a rough surface is, give its assumption (2)

Answer 5

⇒ Rough surface: A surface that is not smooth there is friction (1)
⇒ Objects in contact with a surface experience a friction force (1)

Question 6

Give two assumptions of a smooth and light pulley (2)

Answer 6

⇒ Pulley has no mass (1)

⇒ Tension is the same on either side of the pulley (1)

Question 7

State the assumption correlated with air resistance (1)

Answer 7

⇒ Air resistance is negilible (1)

Question 8

State three assumptions due to gravity. (3)

Answer 8

⇒ Assume all objects with mass are attracted towards the Earth (1)
⇒ Earth’s gravity is uniform and acts vertically downwards (1)
⇒ g is constant as 9.8 m s⁻² (1)

Question 9

State the SI unit for mass. (1)

Answer 9

⇒ Kg

Question 10

State the SI for length/displacement (1)

Answer 10

⇒ meters (m)

Question 11

State the SI unit for time. (1)

Answer 11

⇒ Seconds (s)

Question 12

State the SI unit for speed/velocity. (1)

Answer 12

⇒ m s⁻¹

Question 13

State the SI unit for acceleration. (1)

Answer 13

⇒ m s⁻² (1)

Question 14

State the SI unit for weight/force. (1)

Answer 14

⇒ Newtons (N)

Question 15

Explain how you would convert Km/h ⇒ m/s (3)

Answer 15

⇒ Set up your fraction: Km/h ⇒ m/s
⇒ For nume, convert number from km to m = x by 1000
⇒ For deno, must do the opposite operation of the normal, so
h ⇒ s = x 3600, but you must do ÷ 3600