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What is the difference between longitudinal and transverse waves? Give an example of each How much power is dissipated by the circuit to the right. ( Eq : P = I 2 R = I V) What is the current through the 2-ohm resistor below? . Homework : (55 points) 92 review problems. Types of Waves.

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slide1

What is the difference between longitudinal and transverse waves? Give an example of each

  • How 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?

Homework:

(55 points) 92 review problems

types of waves
Types of Waves

Transverse wave:

medium vibrates at right angles to the direction the energy moves

λ

Compression wave:

(longitudinal wave)

medium vibrates in the same direction as the direction the energy moves

electromagnetic waves
Electromagnetic Waves
  • Mechanical waves require a mediumin order to travel.
    • examples:
  • electromagnetic waves do not require a medium

water,

earthquakes,

and sound

2 how much power is dissipated by the circuit below
2. How much power is dissipated by the circuit below?

Given

Equation 1

Equation 2

R = 200 Ω

V = I R

P = I V

V = 100 V

3 what is the current through the 2 ohm resistor below
3. What is the current through the 2-ohm resistor below?  

Equation

V = I R

Given

R1 = 2 Ω

V = 10 V

Parallel circuit:

Voltage is equal at both resistors

slide8

How 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?

Homework:

(55 points) Finish Review Problems

(6) Reading Log 501-503

slide9
Quiz!
  • Clear your desks!
  • Grab a pencil!
  • Get ready!... Get set!….

GO!

momentum1
Momentum
  • What is the difference between kicking a:
    • stationary ball?
    • ball travelling towards you at 30 mph?
  • Newton solution: moving inertia
momentum2
Momentum

vector

(direction is important)

  • Units:

kgm / s

momentum3
Momentum
  • Let’s try it:
  • momentum of a 50kg person walking at 2 m/s
  • momentum of a speeding bullet

which would you stand in front of?

danger
Danger
  • Why does bullet have more effect?
  • energy of a walking person
  • energy of a speeding bullet

energy!

physics of soft
Physics of “Soft”
  • Falling can have different results
  • Hard landing:
  • Soft landing: able to walk away
  • What’s the difference?

Broken bones, pain…

Phew!

How you change the momentum

changing momentum
Changing Momentum
  • Let’s connect the force to momentum:
  • Substitute with

impulse

  • Impulse is the change in momentum
changing momentum1
Changing Momentum
  • Physics 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 landing
changing momentum2
Changing Momentum
  • Which kid hits the ground faster?
        • both land with same speed:
  • At the bottom, they both have the same momentum:
changing momentum3
Changing Momentum
  • In 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
changing momentum4
Changing Momentum
  • Kid 1
  • Kid 2
  • A pound is about 4Newtons, so
  • Kid 1 feels about 2,000lbs
  • Kid 2 feels about 100lbs

(broken bones)

(piggy back ride)

changing momentum5
Changing Momentum
  • Kid 1
  • Ft
  • Kid 2
  • Ft
  • You can always make a soft change if the impulse time is long enough
time to practice
Time to Practice

Go to pg. 506

physics of catastrophe
Physics of Catastrophe
  • Catastrophic event:
    • collisions
    • explosions
  • In order to know the velocity after, you need to know the momentum before
conservation of momentum
Conservation of Momentum
  • Main reason Newton used
  • It is conserved!
  • So, all the total momentum before something explodes
  • Is thesame after it explodes!
conservation of momentum1
Conservation of Momentum
  • But initially it was not moving!
  • Since momentum is a vector:
  • All of the xvectors add to zero
  • All of the y vectors add to zero
conservation of momentum2
Conservation of Momentum
  • Same for crashes
  • All the momentum before the crash
  • Is the same after the crash
  • Let’s try one…
slide28

Example

A 65 kg swimmer runs with a horizontal velocity of 5.6 m/s off a dock

He 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)

slide29

Example

  • A 65 kg swimmer runs with a horizontal velocity of 5.6 m/s off a dock
  • He 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?
  • Start by drawing a diagram for before and after

vf

vf

or

diagram
Diagram
  • Before:
  • After:

notice the subscripts

How will v1f compare to v2f?

set up conservation equation
Set up conservation equation

only one vf

which direction is vf?

try this out
Try 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)