OPENING QUESTIONS: Let's say you are a runner here on the GHHS Track Team and Eager enters you in the 400 m. That is exactly and precisely 1 lap of a regulation track.
You run your heart out, you finish gasping, legs cramping, lungs about to burst and Coach slaps you on the back and congratulates you on running a PR (Personal Record).
A senior on the team happens to be walking by and says:
"Yeah, but you didn't do ANY real Work at all, just go ask Mr W".
The next day in physics you ask me about the situation and I say "Yep! The senior is absolutely correct. You didn't do any work at all!"
What's going on?
LEARNING OBJECTIVES:
1) I will be able to calculate basic energy problems during today's class.
WORDS O' THE DAY:
- Work (Force through displacement, usually measured in Nm)
- Energy (measured in Joules)
- Power (measured in Joules/sec = Watts)
FORMULAE OBJECTUS:
Work = ∆E = Fd = Fdcosθ
Kinetic Energy = Energy of Motion = KE = 1/2mv2
Gravitational Potential Energy = Ug = mgh
Power = P = energy/time
WORK O' THE DAY:
What are the units of measure of KE?
What are the units of measure for Ug?
In order to change an object's energy, we must do Work on that object.
Write a mathematical equation for that statement
Write the trig version of the definition of work
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Imagine a basketball sized meteor (mass = 56 kg) composed of iron & nickel streaking through the Earth's atmosphere at about 30,000 mph.
Calculate the kinetic energy that meteorite has at that moment.
Now let's further say that ALL of the KE is converted into heat as the meteor explodes on impact in an uninhabited part of the world and the energy is released in .01 seconds. How much power was released on impact?
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Now image a regular ol' basketball (mass = .62 kg). How much gravitational potential energy (Ug) does that basketball have as it is sitting there motionless on a basketball court?
How much work do you have to do on that basketball to lift it up to a height of 1.75 meters (where you hold it motionless) while moving the basketball at a constant velocity?
How much energy does the basketball have then?
Now let's say you drop the basketball, in terms of Ug and KE describe how the energy of the basketball changes as it falls.
How can we use that relationship to find how fast the basketball is going in the tiniest fraction of a second (remember that?) before it hits the ground?
Do it!
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- Please now continue working with those Physics Classroom problems below:
Problems #6 & 7 are fairly basic
Problem #8 is fairly tough
Problem #9 is an elegant beast
and then work on at least half of the following: 16, 17, 22, 24, 25, 28, 31 & 32
And my worked solutions will be HERE