Chapter 15: Momentum, Collisions and Impulse.

Question 1

What should we always do to make Momentum, Impulse and Collision Questions easier?

Answer 1

Draw an image of what is actually happening with labels.

Question 2

What is the equation for Momentum involving Mass and Velocity?

Answer 2

Momentum = Mass x Velocity.

Question 3

What is the equation for the Conservation of Momentum?

Answer 3

Momentum Before = Momentum After - m1u1 + m2u2 = m1v1 + m2v2.

Question 4

What is the meaning of when particles coalesce?

Answer 4

Particles collide and stick together (meaning they have a combined mass and same velocity).

Question 5

If 2 particles are connected by a light, inextensible string, do they have the same speed or different speed?

Answer 5

Same Speed - one pulls the other along.

Question 6

What happens to connected particles once the string between them becomes taut?

Answer 6

The back one ‘catches up’ with the front particle and they collide.

Question 7

What is the letter ‘e’ used for in collisions?

Answer 7

The Coefficient of Restitution.

Question 8

What range of values does the constant ‘e’ have for collisions (restitution)?

Answer 8

0 ≤ e ≤ 1.

Question 9

What does it mean if ‘e’ (coefficient of restitution) has an exact value of 0 (zero)?

Answer 9

The impact of the particles is inelastic (no rebound - they will stick together).

Question 10

What does it mean if ‘e’ (coefficient of restitution) has an exact value of 1?

Answer 10

The impact is perfectly elastic - they will bounce without losing speed.

Question 11

What 2 components make up the speed of approach?

Answer 11

Ua - Ub (Initial Velocity of a - Initial Velocity of b).

Question 12

What 2 components make up the speed of separation?

Answer 12

Vb - Va (Final Velocity of b - Final Velocity of a).

Question 13

What formula can be used to calculate the value of ‘e’ (constant of restitution)?

Answer 13

e = Speed of Separation/ Speed of Approach (v2 - v1/ u1 - u2).

Question 14

What formula can be used to calculate the value of ‘e’ (constant of restitution) on a smooth surface?

Answer 14

e = Speed of rebound of particle (v)/ Speed of approach of particle (u).

u = v = 0 (no friction is involved as the surface is smooth).

Question 15

What does it mean by successive collisions?

Answer 15

Particles collide with another particle and then they collide again with another and so on…

Question 16

What does it mean by successive rebounds?

Answer 16

A particle will have multiple rebounds with a surface (e.g if a ball is dropped vertically, it will bounce back up several times).

Question 17

What is the definition of an impulse?

Answer 17

An impulse is the change of momentum of an object when the object is acted upon by a force for an interval of time.

Question 18

What is the equation for Impulse?

Answer 18

I = Ft –> Impulse = Force x Time.

or change in Momentum –> I = mv - mu.

Question 19

What are the units of Impulse?

Answer 19

Newton Seconds (Ns).

Question 20

What is the equation to find Impulse with a Variable Force?

Answer 20

I = ∫F dt.