Warm Up 1/30/08

1) A 40 kg child is rollerblading down a hill at 15 m/s. What is the momentum of the child?2) A 20 N force acts on a 5 kg object for 4 s, what is the change in velocity of the object?

Standards P 3.3B – Predict how the change in velocity

of a small mass compares to the change in velocity of a large mass when the objects interact (e.g. Collide).

P 3.4F – Calculate the changes in velocity of a thrown or hit object during and after the time it is acted on by the force.

Go over Homework

Pg 217 (1, 4, 12, 13, 16, 18, 22-28 even, 31)

Law of conservation of momentum

Whatever the momentum of a closed system is before an impact, it will be the same after the impact. What's a “closed system”?

mini-lab

Example

A 5 kg bowling ball moving at 2 m/s hits a 0.2 kg tennis ball which is not moving. If the velocity of the tennis ball after the impact is 20 m/s what are:

A) The momentum of the Bowling ball before the collision?

B) The momentum of the Tennis ball before the collsion?

C) The momentum of the system before the collision?

Example Continued

D) The momentum after the collision? E) The momentum of the tennis ball after the

collision? F) The momentum of the Bowling ball after

the collision? G) The velocity of the bowling ball after the

collision?

Practice

2. A 1000 kg car, traveling 22 m/s, hits a 6000 kg bus traveling 15 m/s in the same direction. After the collision the car is traveling 3 m/s.

A) The momentum of the car before the collision?

B) The momentum of the bus before the collsion?

C) The momentum of the system before the collision?

Practice

D) The momentum after the collision? E) The momentum of the car after the

collision? F) The momentum of the bus after the

collision? G) The velocity of the bus after the collision?

Warm Up

Bumper car A has a mass of 150 kg and a velocity of 3 m/s when it hits bumper car B. Bumper car B was traveling 2 m/s, and has a mass of 105 kg. If Bumper car A ends up with a velocity of 1 m/s, what velocity does car B end up with?

What does this mean?

Conservation of momentum.... Astronauts in space ______________ Rockets ______________.

A 10,000 kg rocket expels 10 kg of gas at 20,000 m/s. What will be the change in the velocity of the rocket?

2D collisions

momentum is conserved in each direction independently.

How to solve: Find x direction momentum. Find y direction momentum. - Use conservation of momentum in

each direction. Use pythagorean Thm. To find velocity if needed.

Inverse Trig.

ArcSin or (Sin-1)ArcCos or (Cos-1)ArcTan or (Tan-1)

Example

Billiard balls have a mass of 1 kg. If one billiard ball is traveling forward at 5 m/s and hits the other one, which is at rest, so that the second ball travels away at a 30 degree angle with a velocity of 3 m/s, what is the velocity and the direction of travel (angle) of the first ball.

Practice

2 Bowling balls have a mass of 6 kg. If one bowling ball is traveling forward at 9 m/s and hits the other one, which is at rest, so that the second ball travels away at a 50 degree angle with a velocity of 2 m/s, what is the velocity and the direction of travel (angle) of the first ball.

Homework

pg 217 (6-8, 35-37, 42, 44)