Unit 3: Momentum

Terminology

100

What is an elastic collision?

A bouncy collision

200

What is an inelastic collision?

A sticky collision

300

True or false.

An external force will not produce a change in the momentum. 

False. It will produce a change in the momentum.

400

What is the law of conservation of momentum?

In the absence of an external force, the momentum of a system remains unchanged. 

500

True or false.

Impulse is the measure of how much a force changes the momentum of an object.

True

Basic Momentum

100

What is the Momentum of a 500 kg car traveling at 12 m/s?

p = 6000 kgm/s

200

An athlete has a momentum of 210 kg ∙ m/sec.  If her mass is 50 kg, what is her velocity?

V = 4.2 m/s

300

A toy train has a momentum of 0.72 kg m/s.  When it is going 0.6 m/s, what is its mass?

m = 1.2 kg

400

A car of mass 1500 kg is moving with a velocity of 10 m/s when the brakes are applied for 5 seconds.  At the end of the 5 second period the car has slowed to a speed of 5 m/s.

What was the momentum of the car before the brakes were applied?

p=15,000 kg m/s

500

A car of mass 1500 kg is moving with a velocity of 10 m/s when the brakes are applied for 5 seconds.  At the end of the 5 second period the car has slowed to a speed of 5 m/s.

What was the momentum of the car after the brakes were applied for the 5 second period?

p=7500 kg m/s

Elastic/Inelastic Collisions

100

Two carts collide on a frictionless track. Cart A has a mass of 2 kg and is moving to the right at 4 m/s. Cart B has a mass of 3 kg and is moving to the left at 2 m/s.

Find the final velocities of both carts after the collision.

Cart A (2 kg) ends up moving left at 3.2 m/s

Cart B (3 kg) ends up moving right at 2.8 m/s

200

Two pool balls collide. The first at 0.16 kg is travelling at 2 m/s and the second at 0.18 kg is stationary. After the elastic collision, the first ball is moving at only 0.1 m/s and the second ball continues on toward the corner pocket. How fast is the second pool ball moving?

v₂' =[0.304 kgᐧm/s] / 0.18kg = 1.68 m/s

300

If an 800 kg sports car slows to 13 m/s and a 1200 kg pick up truck behind him continues travelling at 25 m/s, with what velocity will the two move if they lock bumpers after a rear end collision?

What is V_f^'

v_f' =20.2 m/s forward

400

A 4 kg cart traveling to the right at 5 m/s collides with a 2 kg cart traveling to the right at 2 m/s. The carts collide and stick together. Find the speed of the carts after the collision. 

Find V_f^'

v_f' =4 m/s forward

500

A 1.5 kg cart moving at 3 m/s to the right collides with a 2.5 kg cart that is initially at rest. After the collision, the two carts stick together and move as one object.

Find their final velocity after the collision.

The two carts move together at 1.125 m/s to the right after the collision.

Equations

100

Fix the equation:p = m/v

p = m x v

200

J = ?

J = F x t or m(v_f - v_o)

300

Fix the equation:

m₁v₁ + m₂v₂ = m₁v₁² + m₂v₂²

m₁v₁ + m₂v₂ = m₁v₁^' + m₂v₂^'

400

Is this equation for elastic or inelastic collisions?

m₁v₁+m₂v₂ = (m₁+m₂)v_f^'

Inelastic collisions

500

What are the two inelastic equations? 

m₁v₁+m₂v₂ = (m₁+m₂)v_f^'

(m₁+m₂)v_o = m₁v₁^' + m₂v₂^'

Bonus

100

What does the p stand for in the equations?

p = momentum

200

What does the m stand for in the equations?

m = mass

300

What does the v stand for in the equations?

v = velocity

400

What is the unit for momentum?

Kg m/s

500

What are the two collision types?

Elastic (Bouncy) and Inelastic (Sticky).