LEARNING TARGET: I will be able to use The Law of Conservation of Energy to solve motion problems 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:

• U_g = mgh
• KE = 1/2mv²
• TME = U + KE
• W = Fd = Fdcosθ = ∆E
• ∆E = 0
• ∆KE + ∆Ug = 0 (when friction is absent)

ASTRONOMY/VIEWING CALENDAR

is HERE

WORK O' THE DAY:

Lab Returns

Science Pathways - Registration

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Power Practice: The Grand Coulee Dam in Northeastern Washington can produce 8,000 megawatts of power.

• If the average home in Washington State consumes 2.5 kw of power, for how many typical homes can the Grand Coulee Dam provide power?

• If a typical smart phone consume 1.5 watts of energy, how many smart phones could that dam provide power for (assuming of course all the power went into smart phones, which is kinda silly)

• If ALL of that power could be converted in kinetic energy for our favorite 2.58 kg bowling ball, please calculate the final velocity of such a bowling ball.

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BACK To Energy!

A monkey sits on the top of a Sequoia Tree in Northern California playing a harmonica. A less friendly monkey doesn't quite like the tune so he beans the first monkey with a pine cone.

The first monkey then drops the harmonica.

Sketch that situation showing the TOTAL MECHANICAL ENERGY in general terms (such as 100%, gaining, losing, 0%) initially, half way through its fall and again at the tiniest moment before it hits the ground if we ignore air friction.

Now please work with your team to work with the initial conditions shown below to find the greatest velocity the harmonica achieves as it falls from that high tree branch:

• height of the tree = 125 m
• mass of the harmonica = 100. g

Trying to find final velocity

Show equations:

∆E = 0

∆KE + ∆U_g = 0 (when friction is absent)

Rewrite showing each type of Energy

(KE_f - KE_i) + (U_gf - U_gi) = 0

Rewrite using formulae for KE and U_g

(1/2 mv_f² + 1/2 mv_i²) + (mgh_f - mgh_i) = 0

Set appropriate term(s) to 0

(1/2 mv_f² + 1/2 mv_i²) + (mgh_f - mgh_i) = 0

Rearrange and factor appropriate terms

1/2 mv_f² = mgh_i

Cancel common term:

1/2 mv_f² = mgh_i)

Isolate:

v_f² = 2gh_i

v_f = SqRoot(2gh_i)

Substitute:

v_f = SqRoot(2(9.81m/s/s)(125.m))

Solve:

.

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Now let's return to our Physics Classroom problem set. I've added a few to yesterdays set so please feel free to pick and choose problems to work on:

Please ignore Problem #15.

I've marked problems involving friction in PINK. Step over those for now.

And my worked solutions are HERE

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 we haven't learned quite yet) & 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 we haven't learned quite yet)

Problem #31 is difficult. It requires an understanding of friction that we haven't yet learned about

Problem #32 is also fairly rigorous, but really kinda cool!