Before Class Begins Turn in homework (pgs 201 & 204) Get: Whiteboard / pen Calculator Green Sheet (if desired) Notebook / writing instrument

Whiteboard Task If you stand on a skateboard and throw a massive object forward, what happens to your motion? Why does this happen? Use the word momentum in your explanation. What happens if you go through the throwing motion, but don’t let go of the ball? Why?

Homework Correction Practice B: Page 201 1. 380 N to the left (-380 N) 2. 1,100 N upward 3. 16 kg m/s to south (-16 kg m/s) 4a. 9.0 m/s to the right 4b. 15 m/s to the left

Homework Correction Section Review Page 204 1a. p increases by a factor of 2 1b. KE increases by a factor of 4 2a. 31.0 m/s 2b. The bullet 3a. 2.6 kg m/s downfield 3b. 130 N downfield 4. No, it also depends on the time interval 5. Impulse is equal to the change in momentum

Quiz 2f What is the formula for momentum? What is the formula for impulse? How are impulse and momentum related? How does an air bag in a car help save lives (in terms of impulse) A constant force of 6 N acts on a stationary 3 kg object for 10 s. a. What is the change in the object’s momentum? b. What is the change in the object’s velocity?

Collisions and Conservation of Momentum

Objective Identify different types of collisions Solve conservation of momentum problems for a variety of collisions

Vocabulary Collision: an interaction between two or more objects (generally running into each other and either “bounce” or “stick”) Can also include explosions (when two or more connected objects separate)

Types of Collisions Perfectly Elastic Collision: When objects collide without being permanently deformed and without generating heat. Perfectly Inelastic Collision: When colliding objects become tangled or coupled together. Explosions: When two or more connected objects separate due to an internal action

Where will I see these in my everyday life? Elastic Collisions Playing pool Car accidents* Inelastic Collisions Football Explosions fireworks

Solving Problems Law of Conservation of Momentum p1 + p2 before = p1 + p2 after This means Elastic m1v1 + m2v2 before = m1v1 + m2v2 after Inelastic m1v1 + m2v2 before = m12v12 after Explosions m12v12 before = m1v1 + m2v2 after

Perfectly Elastic Collision Example Each croquet ball in a set has a mass of 0.50 kg. The green ball, traveling at 12.0 m/s, strikes the blue ball, which is at rest. In the absence of friction, what is the velocity of the blue ball if the green ball continues moving in the same direction with a speed of 2.4 m/s after the collision. 9.6 m/s

Perfectly Elastic Practice High speed photos show the head of a 215 g golf club traveling at 55.0 m/s just before striking a 46 g golf ball at rest on a tee. After the collision, the club travels (in the same direction) at 42.0 m/s. What is the final speed of the golf ball?

Perfectly Inelastic Example A 6 kg fish swims at 1 m/s toward a 2 kg fish that is at rest and swallows it. What is the velocity of the larger fish immediately after lunch? ¾ m/s

Perfectly Inelastic Practice An 85.0 kg fisherman jumps from a dock into a 135 kg rowboat at rest on the west side of the dock. If the velocity of the fisherman is 4.30 m/s to the west as he leaves the dock, what is the final velocity of the fisherman and the boat?

Explosion Example: A 4 kg model rocket with fuel at rest is launched shooting .05kg of burned fuel from its exhaust at a speed of 625 m/s. What is the velocity of the rocket after the fuel has burned? (ignore gravity and air resistance) -8 m/s

Explosion Practice Two campers dock a canoe. One camper has a mass of 80kg and moves forward at 4.0 m/s as she leaves the boat to step onto the dock. With what speed and direction do the canoe and the other camper move if their combined mass is 115 kg? -3 m/s

Collisions and Kinetic Energy KE is conserved in perfectly elastic collisions KE is NOT conserved in inelastic collisions Some of the KE is converted into heat, sound, or other non-mechanical energy Total Energy, however is ALWAYS conserved!

Independent Practice Practice F (page 216) 1-3 Practice G (page 219) 1-3 Section Review (page 220) 1, 4, & 5