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Efficiency

100

What is Efficiency?

Ratio of output work to input work

200

How much work do you get out of a machine?

Less than you put into a machine. 

300

What is the efficiency of a machine that does 800 Joules if the input work of the machine is 2000 Joules. 

(800Joules)/(2000 Joules) = .40

.40 x 100 = 40% efficient

400

What are the three ways machines can be useful?

Increase speed, increase force, and change direction of force

500

The input work on a pulley system is 75J. If the pulley system is 84% efficient, then what is the output work form the pulley system?

84% = [(x)/(75Joules)] x 100%

.84 = (x)/(75Joules)

x = (.84) x (75Joules) 

63 Joules = output work

Efficiency 2

100

What are the proper units for the Efficiency formula?

Efficiency = %

Output and Input Work = Joules

200

What is the formula for an efficiency calculation?

e= (work_out)/(work_in) x 100%

300

What is the formula for Mechanical Advantage?

MA = Force_out / Force_in

400

A crate weighs 950N. If you can use a pulley system to lift that crate with a force of only 250N, then what is the mechanical advantage of the pulley system?

950N/250N = 3.8MA

500

The output work on a pulley system is 45J. If the pulley system is 77% efficient, then what is the input work from the pulley system?

77% = [(45 Joules)/(x)] x 100%

.77 = (45 Joules)/(x)

x = (45 Joules)/ (.77)

58.44 Joules is the input work

Energy 1

100

Regardless of what kind of energy it is, energy can be categorized into what two general categories?

Kinetic or Potential Energy

200

What is an example of a sytem?

Two people playing ping pong, the solar system, etc. 

300

Why is Energy also measured in Joules?

Because energy can be described as the ability to do work

400

What are the four main forms of energy?

Mechanical, Electrical, Chemical, Radiant

500

What does "Energy is Energy" mean?

Energy does not have a set form. Energy can take many different forms but regardless of its form it is still energy, it doesn't turn into something else other than energy

Energy 2

100

What it is an example of Kinetic Energy?

Something moving

200

What is the formula for Kinetic Energy?

KE = 1/2mv²

300

What are the correct labels for a Kinetic Energy calculation?

Kinetic Energy = Joules

Mass = kg

V = m/s

400

A jogger with a mass of 60.0kg is moving forward at a speed of 3.0 m/s. What is the jogger’s kinetic energy from this forward motion?

KE = 1/2(60.0kg)(3.0m/s)²

KE = 1/2(60.0kg)(9.0m²/s²)

KE = 270 Joules

500

A baseball had a kinetic energy equal to 400 Joules. The baseball has a mass of 20.0kg. How fast must the baseball have been moving to have a kinetic energy of 400 Joules?

400Joules = 1/2(20.0kg)(x)²

800 = (20.0kg)(x)²

40 = x²

6.325m/s

Energy 3

100

What is an example of Potential Energy?

Food, unburned fossil fuels, something sitting on a shelf, stretching a rubber band, etc. 

200

What is the formula for gravitational potential energy?

GPE = mgh

300

What are the proper units for a gravitational potential energy calculation?

Mass = kg

gravity = n/kg

height = m

400

A 4.0Kg ceiling fan is placed 2.5m above the floor. What is the gravitational potential energy of the Earth-Ceiling fan system relative to the floor.

(4.0kg)(9.8N/kg)(2.5m)

98 Joules

500

If the gravitational potential energy of a baseball is 77Joules and the baseball weighs .5kg, what height must the baseball be compared to the ground?

77 Joules = (.5kg)(9.8N/kg)(X)

15.71 meters above the ground