Plan for Today (AP Physics 1). Go over MC Go over Momentum Review HW: Study for Test Tomorrow. Apply the impulse momentum equations and describe how the concept of impulse “cushions” a collision. I = change in P F * t = m * change in v
Plan for Today (AP Physics 1)
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Apply the impulse momentum equations and describe how the concept of impulse “cushions” a collision
I = change in P
F * t = m * change in v
Longer time means less force for the same change in momentum
This is the cushioning effect
Calculate the impulse or change in momentum given a force time graph
Area under curve = Impulse (F * t)
Impulse = Change in Momentum
Be able to figure out velocities from a graph
I = change in momentum = m * change in v = m * (vf – vi)
Apply conservation of momentum
M1v1i + m2v2i = m1v1f + m2v2f
You will be given enough to solve for an unknown
Make sure to note if masses are together at the beginning or the end of a collision
Remember, you can’t use conservation of energy for inelastic collisions
Apply conservation of momentum and conservation of kinetic energy to elastic collisions
Pi = Pf
For elastic collisions, kinetic energy is also conserved
Kei = Kef
Solve a ballistic pendulum problem
Two stages to this
Bullet collides with pendulum
Conservation of momentum
M1v1i + m2v2i = m1v1f + m2v2f
Pendulum rises into the air
Conservation of Mechanical Energy
KEi = Peg
Be careful with when masses are together and when to treat separately
Define elastic, perfectly inelastic, and inelastic collisions
Elastic – objects collide and bounce off each other
Momentum is conserved
Kinetic energy is conserved
Objects collide and get stuck together
They continue to move together at the same speed
Momentum is conserved, but not KE
Inelastic collisions – momentum is conserved, some kinetic energy is changed to another force of energy
Calculate the change in momentum of a two dimensional collision
Have to break up into x and y
Momentum will be conserved
Still Pi = Pf, just two times
Momentum example problems
Ballistic Pendulum Problem
Using a graph of force vs. time to make calculations (area under curve)
Basic momentum, conservation of momentum, and impulse calculations
Formulas you will use
In class, Ms. Knittig fired a PVC bullet (200 g) at a pendulum (2.1 kg). The pendulum (with the bullet inside) rose 17 cm in the air. What was the original velocity of the bullet?
In a pool game, a green billiard ball travels north at 2.1 m/s. It collides with another red ball traveling at 1.2 m/s south. After the collision, the green ball travels south at 1.3 m/s. What is the velocity of the red ball?
A child plays with a toy train set. He pushes a 150 g train with a velocity of 2.3 m/s into two cars (each with mass 125) that are at rest stuck together. All three get stuck together and continue to travel. What is the final velocity of the train set?
Daisy the dog applies a force of 2.5 N to her 120 g bone for .13 seconds to launch her bone in the air. What is the velocity of her bone after the push?
Daisy the dog’s bone collides with the wall with an initial velocity of 5.1 m/s. It leaves the wall traveling at 4.2 m/s. The bone still has a mass of 120 g. What is the change in momentum of her bone?
If the bone is in contact with the wall for .09 seconds, what is the force applied on her bone?