W8 Coefficient of Restitution

Question 1

What are the two types of collisions and what is different about them?

Answer 1

1. Inelastic Collision
   - Momentum is conserved but kinetic energy is lost
   - Colliding objects stick together and can be treated as one, post collision
2. Elastic Collision
   - Momentum is conserved
   - Kinetic energy is conserved

Question 2

Are all collisions exactly inelastic or elastic collisions?

Answer 2

• No, most of the time collisions are not perfect elastic or inelastic collisions
  E.g. Colliding objects do not stick together + Kinetic energy is not fully conserved (heat & sound)

Question 3

What is the equation for Coefficient of Restitution (e)?

Answer 3

• The square root of kinetic energy after collision divided by kinetic energy after collision.

Question 4

• If you throw a ball down at earth what is earth’s velocity?

Answer 4

• It’ll be 0 because it isn’t moving + collisions with earth will include acceleration because of gravity

Question 5

How do you work out Post collision?

Answer 5

• Best way to work this out is to work out the post collision is using a SUVAT equation but using ‘g’ instead of acceleration which is acceleration due to gravity (9.81)

Question 6

What is the definition of friction?

Answer 6

• When one body moves across the surface of another body. The opposing force is friction

Question 7

What are the the two types of friction and describe them?

Answer 7

1. Sliding friction
   - The opposing friction between two sliding objects in motion
2. Rolling friction
   - The frictional force that occurs when one object rolls over another one

Question 8

What is the coefficient otherwise known as?

Answer 8

u or Mu

Question 9

What are the three factors you need to calculate sliding friction?

Answer 9

P = force applied
R =  Reaction force (normal / perpendicular to constant surface)
F = friction force

Question 10

What are the three factors you need to calculate sliding friction?

Answer 10

P = force applied
R =  Reaction force (normal / perpendicular to constant surface)
F = friction force

Question 11

What does U mean?

Answer 11

U is the Dimensionless Scalar Value

Question 12

What does U mean?

Answer 12

U the coefficient of friction which is a Dimensionless Scalar Value
- This describes the ratio of the force friction and the normal (perpendicular) force between the bodies

Question 13

Give some factor that limit friction:

Answer 13

• Contacting surface area

- Reaction force

Question 14

When a little ‘s’ gets added to the equation it shows that…

Answer 14

• It shows that forces are sliding during the equation

Question 15

The coefficient of sliding friction < coefficient of limiting friction
OR
The coefficient of sliding friction > coefficient of limiting friction

Answer 15

This is the correct answer:

The coefficient of sliding friction < coefficient of limiting friction

Question 16

If ‘P’ (force applied) exceeds ‘F’ (friction force) then what happen’s to the object?

Answer 16

• When ‘P’ exceeds ‘F’ sliding occurs

Question 17

What branch of mathematics do you use to calculate the coefficient of limiting friction?

Answer 17

• Trigonometry

Question 18

The coefficient of limiting friction is equal to the tangent of what?

Answer 18

• Coefficient of limiting friction is equal to the Tangent of theta. At the point where the objects started to slide.