3. Conservation of Momentum Elastic

3. Conservation of Momentum Elastic

Multiple Choice

The cherries:

What kind of collision is this?

• Elastic

• Inelastic

• Explosion

Multiple Choice

Both pucks have a mass of 1.0 kg. Puck A is at rest and puck B comes in at 2 m/s. What is the momentum of A and B?

• A: 0 kg⋅m/s

  B: 2 kg⋅m/s

• A: 2 kg⋅m/s

  B: 0 kg⋅m/s

• A: -2 kg⋅m/s

  B: 2 kg⋅m/s

• A: 0 kg⋅m/s

  B: 0 kg⋅m/s

Multiple Choice

What is the total momentum of this system? (add them)

• 2 kg⋅m/s

• 0 kg⋅m/s

• That's not possible

Multiple Choice

What happens AFTER they collide?

• Both stop moving

• Both move together in the direction that puck B was moving, just slower

• Puck B stops and puck A moves to the right instead

• Puck A stays put and puck B bounces back

Multiple Choice

NOW They’re both moving towards each other: Puck A at 1 m/s and puck B at 2 m/s.

Calculate the momentum of each puck

• p_A = 2 kg⋅m/s

  p_B = 1 kg⋅m/s

• p_A = 1 kg⋅m/s

  p_B = 2 kg⋅m/s

• p_A = -1 kg⋅m/s

  p_B = 2 kg⋅m/s

• p_A = -2 kg⋅m/s

  p_B = 1 kg⋅m/s

Multiple Choice

What is the total momentum of the system of both pucks?

• p_total = 2 kg⋅m/s

• p_total = 0 kg⋅m/s

• p_total = 1 kg⋅m/s

• Can't tell

Multiple Choice

What happens AFTER they collide?

• Both stop moving

• Both move together in the direction that puck B was moving, just slower

• Puck B stops and puck A moves instead

• Puck A moves to the right and puck B bounces back

Multiple Choice

Now what if puck A is not moving again but I triple the mass of puck B (m=3kg)?

What is the total momentum of the system of both pucks?

• p_total = 3 kg⋅m/s

• p_total = 6 kg⋅m/s

• p_total = 2 kg⋅m/s

• p_total = 0 kg⋅m/s

Multiple Choice

What is going to happen AFTER they collide?

• Both stop moving

• Both move together to the right, and A is faster than B

• Puck B stops and puck A moves instead

• Puck A stays put and puck B bounces back

General Strategy

For solving ANY conservation of momentum problem

Multiple Choice

What is the TOTAL momentum of the bat-ball system?

• p_total = 4.3 kg⋅m/s

• p_total = 30.9 kg⋅m/s

• p_total = 17.6 kg⋅m/s

• p_total = 13.3 kg⋅m/s

Multiple Choice

AFTER the collision, the ball flies away with a speed of 45 m/s. How fast is the bat now?

• v'_bat = - 5.2 m/s

• v'_bat = - 11.45 m/s

• v'_bat = 1.95 m/s

Multiple Choice

Energy due to motion is ____________ energy. 

• Potential 
• Energy
• Kinetic
• Friction

Multiple Choice

The Law of Conservation of Energy states that

• energy cannot be created nor destroyed, only transformed or transferred
• energy can be destroyed but not created
• energy can be created but not destroyed

Multiple Choice

What's the equation for kinetic energy again?

• $\frac{1}{2}mv^2$

• $mgh$

• $mv^2$

• $mv$

Multiple Choice

Do you think KE is conserved in a collision, just like momentum is?

• Yes

• No

In an Elastic Collision, we conserve

• Momentum

• Kinetic Energy

• ALWAYS!!!!!!!!!!!!!!!!!!!!