Mechanics - Elastic Collisions In 2 Dimensions

Question 1

What is NEL

Answer 1

Newtons experimental law (Newtons law of restitution)
e X speed of approach = speed of separation

Question 2

What do you know about the direction of the impulse?

Answer 2

It will be perpendicular to the surface

Question 3

In 2D impacts what do you know is true?

Answer 3

Parallel to wall nothing will happen
Perpendicular to the wall things happen

Question 4

What is the main thing with these 2D questions?

Answer 4

Splitting the speed into its components (cos and sin)
Then saying that perpendicular to the surface NEL applies

Question 5

What is the angle of deflection?

Answer 5

The angle where if you continued drawing the line of original motion and between the new motion

Question 6

What is a good way to find the angle of deflection?

Answer 6

Sing dot products

Question 7

What do you do when the wall isn’t vertical o horizontal?
First answer why you need to do this?

Answer 7

You can’t split into horizontal or vertical components as i and j are parallel and perpendicular to the axis not the wall

You find a vector to model the wall of the impulse. Then state the perpendicular vector. You can then use vectors to split the original speeds into parallel and perpendicular to the wall

Question 8

How may you find out the vectors that are parallel to and perpendicular to the wall?

Answer 8

The Qs may say the wall is parallel to y=x so (11) is the vector
You may be able to calculate the impulse to find a perpendicular vector
You may have to use other methods (Mixed exercise Q13)

Question 9

What vector is perpendicular to (ab)
How can you check?

Answer 9

(-ba)
The dot product should equal 0

Question 10

When working with oblique impacts what direction is the Impulse in?

Answer 10

Along the line of centers

Question 11

What is the important bit of oblique impacts?

Answer 11

Perpendicular to the line of centers nothing will happen

Question 12

What are the 2 things that you need to use in oblique impacts most questions?

Answer 12

Conservation of linear momentum (com)
NEL

Question 13

How do you lay out an oblique impacts question?

Answer 13

Question 14

How do you do oblique impact questions if the line of centers isn’t parallel or perpendicular?

Answer 14

Use the vector method

Question 15

What is an useful thing to remember with the vector method?

Answer 15

You can use the simplified versions of the parallel and perpendicular vectors

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