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MondayQuestion of the Day: How prepared will you be for the final? What do you need to relearn?Agenda:Do NowStart Review ProblemsHomeworkHomework:(55 points) 92 review problemsWhat is the difference between longitudinal and transverse waves? Give an example of eachHow much power is dissipated by the circuit to the right. (Eq: P = I2 R = I V)

What is the current through the 2-ohm resistor below?

1Types of WavesTransverse wave:medium vibrates at right angles to the direction the energy moves

Compression wave:(longitudinal wave)medium vibrates in the same direction as the direction the energy moves

2Types of Waves: http://www.youtube.com/watch?v=Rbuhdo0AZDU

3Music

Electromagnetic WavesMechanical waves require a medium in order to travel.examples:

electromagnetic waves do not require a mediumwater,earthquakes, and sound 2. How much power is dissipated by the circuit below?

GivenR = 200 V = 100 VEquation 1V = I R

Equation 2P = I V

3. What is the current through the 2-ohm resistor below? GivenR1 = 2 V = 10 VEquationV = I R

Parallel circuit:Voltage is equal at both resistors

TuesdayQuestion of the Day: How prepared will you be for the final? What do you need to relearn?Agenda:Quiz Cornell NotesStart Review ProblemsHomeworkHomework:(55 points) Finish Review Problems(6) Reading Log 501-503How much power is dissipated by the circuit to the right. (Eq: P = I2 R = I V)

What is the current through the 2-ohm resistor below?

8Quiz! Clear your desks!

Grab a pencil!

Get ready!... Get set!.

GO! Momentum

10MomentumWhat is the difference between kicking a:

stationary ball?

ball travelling towards you at 30 mph?

Newton solution: moving inertia11Momentum

vector(direction is important)Units:kgm / s12what do you notice about momentum? vector. What does this mean? direction is important.MomentumLets try it:momentum of a 50kg person walking at 2 m/s

momentum of a speeding bullet

which would you stand in front of?

13momentum units: kgm/smomentum can come from something with a small mass going fast and something with a large mass going slow.DangerWhy does bullet have more effect?

energy of a walking person

energy of a speeding bullet

energy!14the large amount of energy in the bullet makes it more dangerousPhysics of SoftFalling can have different results

Hard landing:

Soft landing: able to walk away

Whats the difference?Broken bones, painPhew!How you change the momentum15Changing MomentumLets connect the force to momentum:

Substitute with

impulseImpulse is the change in momentum16Changing MomentumPhysics of soft refers to how momentum is reduced

For example: two 50kg kids jump off a 12 ft (~4 m) building.

Kid 1 lands with straight legs

Kid 2 tucks and rolls when landing17Changing MomentumWhich kid hits the ground faster? both land with same speed:

At the bottom, they both have the same momentum:

18Changing MomentumIn order to stop, their impulse will have to be:

Kid 1 has a really short landing, 0.05 s

Kid 2 makes the landing last longer, 1.0 s

We can use the impulse to find the force each kid feels

19Changing MomentumKid 1

Kid 2

A pound is about 4 Newtons, so

Kid 1 feels about 2,000 lbs

Kid 2 feels about 100 lbs(broken bones)(piggy back ride)

20Changing MomentumKid 1 Ft

Kid 2 FtYou can always make a soft change if the impulse time is long enough

21Time to PracticeGo to pg. 50622Physics of CatastropheCatastrophic event:collisionsexplosions

In order to know the velocity after, you need to know the momentum before

23Main reason Newton used

It is conserved!

So, all the total momentum before something explodes

Is the same after it explodes!Conservation of Momentum

24Conservation of MomentumBut initially it was not moving!

Since momentum is a vector:

All of the x vectors add to zero

All of the y vectors add to zero

25Conservation of MomentumSame for crashes

All the momentum before the crash

Is the same after the crash

Lets try one26

27ExampleA 65 kg swimmer runs with a horizontal velocity of 5.6 m/s off a dockHe jumps into a 15 kg rubber raft that is drifting towards him with a velocity of 1.0 m/s

What is the velocity of the swimmer and raft after the impact? (assume no friction or resistance due to air or water)

28ExampleA 65 kg swimmer runs with a horizontal velocity of 5.6 m/s off a dockHe jumps into a 15 kg rubber raft that is drifting towards him with a velocity of 1.0 m/sWhat is the velocity of the swimmer and raft after the impact?

Start by drawing a diagram for before and after

vfvfor29DiagramBefore:

After:

notice the subscriptsHow will v1f compare to v2f?30Set up conservation equation

only one vf

which direction is vf?31Try this out!Answer questions 89-92 on your review sheet

Turn it in on a separate piece of paper by the end of class

(Disclaimer: These questions do not count as part of your 42 problems) 32