Monday Question of the Day: How prepared will you be for the final? What do you need to relearn? Agenda: Do Now Start Review Problems Homework Homework: (55 points) 92 review problems Homework: (55 points) 92 review problems 1.What is the difference between longitudinal and transverse waves? Give an example of each 2.How much power is dissipated by the circuit to the right. (Eq: P = I 2 R = I V) 3.What is the current through the 2-ohm resistor below? 1.What is the difference between longitudinal and transverse waves? Give an example of each 2.How much power is dissipated by the circuit to the right. (Eq: P = I 2 R = I V) 3.What is the current through the 2-ohm resistor below?

Types of Waves Transverse wave: medium vibrates at right angles to the direction the energy moves Compression wave: (longitudinal wave) Compression wave: (longitudinal wave) medium vibrates in the same direction as the direction the energy moves λ λ

Types of Waves: buhdo0AZDU buhdo0AZDU

Music

Electromagnetic Waves Mechanical waves require a medium in 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? Given R = 200 Ω V = 100 V Equation 1 V = I R Equation 2 P = I V

3. What is the current through the 2-ohm resistor below? Given R 1 = 2 Ω V = 10 V Equation V = I R Parallel circuit: Voltage is equal at both resistors

Tuesday Question of the Day: How prepared will you be for the final? What do you need to relearn? Agenda: Quiz Cornell Notes Start Review Problems Homework Homework: (55 points) Finish Review Problems (6) Reading Log Homework: (55 points) Finish Review Problems (6) Reading Log How much power is dissipated by the circuit to the right. (Eq: P = I 2 R = I V) 2.What is the current through the 2-ohm resistor below? 1.How much power is dissipated by the circuit to the right. (Eq: P = I 2 R = I V) 2.What is the current through the 2-ohm resistor below?

Quiz! FClear your desks! FGrab a pencil! FGet ready!... Get set!…. FClear your desks! FGrab a pencil! FGet ready!... Get set!…. GO!

M OMENTUM

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

M OMENTUM vector (direction is important) Units: kg  m / s

M OMENTUM 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?

D ANGER Why does bullet have more effect? energy of a walking person energy of a speeding bullet energy!

P HYSICS OF “S OFT ” 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

C HANGING M OMENTUM Let’s connect the force to momentum: Substitute with impulse Impulse is the change in momentum

C HANGING M OMENTUM 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

C HANGING M OMENTUM Which kid hits the ground faster? both land with same speed: At the bottom, they both have the same momentum:

C HANGING M OMENTUM 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

C HANGING M OMENTUM Kid 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)

C HANGING M OMENTUM Kid 1 F t Kid 2 F t You can always make a soft change if the impulse time is long enough

Time to Practice Go to pg. 506

P HYSICS OF C ATASTROPHE Catastrophic event: collisions explosions In order to know the velocity after, you need to know the momentum before

Main reason Newton used It is conserved! So, all the total momentum before something explodes Is the same after it explodes! C ONSERVATION OF M OMENTUM

But 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

C ONSERVATION OF M OMENTUM Same for crashes All the momentum before the crash Is the same after the crash Let’s try one…

E XAMPLE 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)

E XAMPLE 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 vfvf vfvf vfvf vfvf or

D IAGRAM Before: After: notice the subscripts How will v 1f compare to v 2f ?

S ET UP CONSERVATION EQUATION only one v f which direction is v f ?

Try this out! Answer questions 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)