OPENING QUESTIONS: Before we dive back into the Physics Today problems, let's take a review swing at a POWER problem.
Let's say that you use your 1250 W hairdryer for 10. minutes.
You are an omnipotent individual so you are able to transfer ALL of that energy into a .45 kg ball on the floor at your feet.
How high would that energy be able to move that ball if we ignore friction?
LEARNING TARGET: I will be able to use The Law of Conservation of Energy to solve motion problems that include energy gained/lost during today's class
WORDS O' THE DAY:
- Work: A transfer or change of Energy
- Gravitational Potential Energy: Energy based on altitude
- Kinetic Energy: Energy of motion based on mass & velocity
- Mechanical Energy = The sum of all potential and kinetic energy in a system
- friction = Heat energy is generated when a moving object transfers some of its energy to individual molecules (such as air)
CALENDAR:
Work, Power & Energy Test on FRIDAY, March 10th.
FORUMULAE OBJECTUS:
- Ug = mgh
- KE = 1/2mv2
- TME = U + KE
- W = Fd = Fdcosθ = ∆E
- ∆E = 0
- ∆KE + ∆Ug = 0 (when friction is absent)
- ∆E = +/- W (when energy is lost or gained)
- ∆KE + ∆Ug = +/- W (when energy is lost or gained)
WORK O' THE DAY:
Opener:
Find the TOTAL amount of energy used (power x time)
Recognized that 100% of that energy will be converted into gravitational potential energy = mgh and solve for h!
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Let's try another power problem:
Let's say you are driving a 1450 kg car that is moving at 55 mph. You hit the brakes and your car stops in a fairly comfy 10. seconds.
How much power did you brakes exert on the wheels of your car?
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Now let's return to our Physics Classroom problem set. Please work on a couple of the pink (friction) problems
Keep in mind that friction is f=μN = μmg
Please ignore Problem #15.
I've marked problems involving friction in PINK. If you keep in mind that friction is a force that can (and does) do work (Work = fd) on an object in motion AND that friction is f=μN = μmg, then you should be able to take a stab at the friction problems.
NOTES: HOPEFULLY you have done a bunch of these already
Problem #10 is fairly general
Problem #11 will have you think but nothing TOO strenuous
Problem #12 & 13 are fairly general
Ignore Problem #15
Problem 16 is a good, challenging problemm...but not TOO nasty
Problem #17 is fairly general
Problem #20 (requires friction which is fun) & 22 are fairly straightforward but the last parts will make you think a bit.
Problem #24 & 25 are fairly general
Problem #28 requires a CLOSE READING of the problem (requires friction which is fun)
Problem #31 is difficult and requires friction which is fun
Problem #32 is also fairly rigorous, but really kinda cool (friction here too)!