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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
- 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
- Perfectly inelastic
- 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
- Explanation of
- Using a graph of force vs. time to make calculations (area under curve)
- Basic momentum, conservation of momentum, and impulse calculations

Example 1

- 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?

Example 2

- 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?

Example 3

- 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?

Example 4

- 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?

Example 5

- 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?

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