tuesday, april 23rd physci · may 8, 2019 tuesday, april 23rd • in class > notes on work >...
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May 8, 2019
Tuesday, April 23rd• In Class
> Notes on Work> Practice equations
• Practice> Work Problems - pg. 90-93
• Upcoming> Work & Power Quiz - Monday April 29th
PhySci
Work & EnergyChapter 13
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May 8, 2019
I. What is WORK?
• Energy applied to an object as a force, in which the object moves in the same direction as the applied force.
• Work ( W ) is measured in ( ), also called joules (J)
• 1 J of work = lifting a 1N apple to top of head.
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May 8, 2019
What is the work when a force of 10 N pulls a 80 N box a distance of 5.0 m across the floor?
What is the work done if the same box is lifted 5 m upward?
Wednesday, April 24th• In Class
> Copy down slide (II) on Power and record the practice question down.
> Practice Work & Power equations
• Practice> Work Problems - pg. 90-93 (answer key uploaded)
> Power Problems - pg. 94-96 (answer key uploaded thursday)
• Upcoming> Work & Power Quiz - Monday April 29th
PhySci
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May 8, 2019
II. What is Power?
• Rate at which work is done or energy is transformed.> work done in a given amount of time
• Power(P) is measured in ( ), also called watt (W)
• 1 W of power = lifting a 1N apple to top of head in 1 s
Lifting an elevator 18 m takes 100 kJ. If doing so takes 20s, what is the average power of the elevator during the process?
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May 8, 2019
Monday, April 29th• In Class
> Work & Power Review> Work & Power Quiz Tomorrow
• Practice> Work Problems - pg. 90-93> Power Problems - pg. 94-96
PhySci
A mechanic uses a hydraulic lift to raise a 1,200 kg car 0.50 m off the ground in 3 seconds. How much power was used to raise the car?
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May 8, 2019
Wednesday, May 1st• In Class
> Mechanical Advantage Notes> Practice, Work/Power/MA Equations
• Practice> Work Problems - pg. 90-93> Power Problems - pg. 94-96> MA Problems - pg. 97-100
PhySci
III. MACHINES
• Machines make work seem easier by changing...> SIZE of an input force> DIRECTION of the force> or both
*Multiplies the input force– creates larger output force over less distance
• Mechanical Advantage: A # that expresses how much a machine multiplies force or distance
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May 8, 2019
A mover uses a ramp to load a 5 kg box into a truck 1.4 m off the ground. The ramp is 4.6 m long (ignore friction) what is the mechanical advantage of the ramp?
Friday, May 3rd• In Class
> Stair Lab
• Practice> Work/Power/MA Problems - pg. 90-100
• Homework> Stair Lab Due Tuesday (5/7)
PhySci
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May 8, 2019
Monday, May 6th• In Class
> Discuss Stair Lab> Begin Energy Notes (3)
• Practice> Work on GPE Problems - pg. 109 - 111
• Homework> Stair Lab due Tuesday 5/7> Study for Ch. 13 Test - Thursday 5/9
PhySci
IV. What is Energy
• Energy is...> the ability to do work> the ability to cause change
– All changes require energy
• Work (J) is the Transfer and/or Transformation of energy from one object to another
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May 8, 2019
V. Mechanical or Not?
• Mechanical Energy> Energy able to do work directly
– Gravitational PE, Elastic PE, Visible KE
• Non-Mechanical Energy> Energy that cannot directly do
work.– Needs to be transformed
into a different form first. » Nuclear, Chemical ,
Electrical, Light, Heat
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May 8, 2019
VI. Potential Energy Energy that is STORED
> has the potential to cause change or do work
• 4 Different Types> 1) Gravitational PE (GPE)
« stored energy due to height of object« GPE (J) = mass (kg) x gravity (m/s2) x height (m)
> 2) Elastic PE« energy stored when an object is not in its original
condition» ex: stretched rubber band, compressed ball
> 3) Chemical PE« energy stored in the bonds of a molecule
> 4) Nuclear PE« energy stored in the nucleus of an atom
Tuesday, May 7th• In Class
> Finish Energy Notes
• Practice> Work on KE Problems - pg. 107 - 109> Work on GPE Problems - pg. 110 - 112
• Homework> Study for Ch. 13 Test: Thursday 5/9
PhySci
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May 8, 2019
A 70,000 g boulder is resting at the top of a 0.1 km cliff. What is the GPE of the boulder?
VII. Kinetic Energy> energy of a moving object which depends on...
– Mass– Speed (velocity)
• Kinetic Energy (J) = 1/2 x mass (kg) x v2 (m/s)– KE = 1/2mv2
• Faster an object moves, more KE it has = bigger crashes....> Same holds true for increasing mass
• 2 types of Kinetic Energy> 1) KE of "visible" objects in motion
> 2) KE of atoms/molecules in a substance
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May 8, 2019
A 46 kg cheetah can run with a max speed of 72 mph. What is its kinetic energy?
Wednesday, May 8th• In Class
> Review Problems> Study for Ch. 13 Test
• Homework> Study for Ch. 13 Test: Tomorrow!!
PhySci
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May 8, 2019
A lever & fulcrum are used to lift a 45.4 kg rock. The lever has a mechanical advantage of 9.50, so what must be the force used on the lever to begin lifting the rock?
A 37 kg Zach can run with a max speed of 11.5 mph. What is his kinetic energy?
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May 8, 2019
What is the power required to push the 10 kg box up the ramp over the span of 8 seconds?