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
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.
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
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?
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?
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
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
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
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
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
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
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
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?
May 8, 2019
What is the power required to push the 10 kg box up the ramp over the span of 8 seconds?
