Download Review for test number 2. Know the definitions of the different types

Review for test number 2.
Know the definitions of the different types of energies.
Give examples of renewable and non-renewable resources and fossil fuels.
Work = force X displacement.
Pull a cart with a force of 120 N for a displacement of 5 m. The work is 120N x 5m = 600 Joules
If there is no displacement there is no work. Also if the force and the displacement are
perpendicular to each other there is no work.
kinetic energy = ½ m v2
work = change in kinetic energy
1 horsepower = 746 Watts.
multiply the number of horsepower by 746 to get the
number of Watts.
example: 50 hp = 37300 Watts
Power = Work/time
example 1:
it takes 6 seconds for a 10 Watt motor to do 60 Joules of work.
example 2:
Find the power by dividing the work by the time. Power = (200000 J)/(6 s) = 33333 Watts
also power = change in kinetic energy / time
example: 1000kg car speeds up from 0 m/s to 20 m/s in a time of 6 seconds.
The change in kinetic energy is: ½ (1000 kg)(20 m/s)2 - ½ (1000 kg)(0m/s)2 = 200000 J
Power = (200000 J)/(6 s) = 33333 Watts
Power can also be described as Force x velocity
Power = Force x velocity
Apply a 60 N force while moving a box 5 m/s. The power is (60N)x(5 m/s)= 300 Watts
gravitational potential energy = mass x gravity x height.
Lower a 50 kg block a distance of 2 meters.
You lowered the gravitational energy by: (50 kg) x (9.8 m/s2) x (2 m) = 980 Joules
When converting potential energy to kinetic energy set up the following equation:
m g h = ½ m v2
Notice that the mass cancels out; this gives: v
2gh
Be able to convert from Celsius to Fahrenheit: TF = (9/5)TC + 32
TC = (5/9) (TF – 32)
Efficiency = useful energy output/energy input
Heat in
also: heat engine efficiency =
Heat exhaust
Heat in
or
1
=
Texhaust
Tin
Heat exhaust = Energyin - Energyout
Examples:
Engine has 200 J of energy input. The engine produces 150 Joules of useful work (or heat).
The exhaust is 200J - 150 J = 50 J
Efficiency = 150/200 = 75 %
200 J of thermal energy goes into an engine. 120 J of energy goes out the exhaust.
efficiency = (200 J - 120 J)/(200 J) = 40 %
Exhaust temperature is 400 Kelvin. Input temperature is 600 K.
Efficiency = 1 - 400/600 = 33 %
Know the difference between internal and external combustion engines.
Look to see what types of transportation are the most efficient.
Know the doubling rule for exponential growth. (Rule of 70)
Doubling time = 70/growth rate
Put money in a savings account that earns 5 % interest annually.
Doubling time = 70/5 = 14 years