Working hard or hardly working?
No one man should have all that Power!
5-Hour Energy
Efficiency Proficiency
The Conservation station
100
Write the formula for Work
W=F*d
100
Write the formula for Power
P=W/t or P=(DeltaE)/t
100
Write the formula for Kinetic energy and the formula for Potential energy
KE=1/2mv^2
U=mgh
100
Write the efficiency formula
% e = ("output")/("input") *100
100
Write the general form of the "Work-Energy Theorem"
W=DeltaE
200
The units of Work are the same as the units of all forms of Energy. What is this unit?
Joules (J)
200
What are the correct units for Power (the rate at which energy is used)?
Watts (W) or Joules per second (J/s)
200
A car (mass=1200 kg) drives at a velocity of 14 m/s. How muhc kinetic energy does the car have?
KE=(1/2)mv2 =
(1/2)(1200)(14)2 = 117,600 J
200
A machine has a power rating of 500 W. How much energy is used in 10 seconds?
P=W/t
500 = W/10
W=5000 J
200
50J of work is done on an object, The change in energy of the object is: _____
W=DeltaE
50J
300
Which forces do work on the block if it is moving horizontally to the right?
Force (F) does positive work
Friction force (fk) does negative work
(Normal force (N) and weight (w) do no work)
300
A lightbulb releases 90 J of energy in 2 seconds. What is the power rating of the machine
P=W/t=(DeltaE)/t
P=90/2 = 45 "Watts"
300
A ball (mass=2kg) is at rest at the top of a hill that is 20 meters high. How much potential energy does the ball have?
U= mgh = (2)(9.8)(20) = 392 J
300
A machine has a power rating of 500 W.How much time would it take for the machine to use 2,000 Joules of energy?
P=W/t
500 = 2000/t
t=2000/500 = 4 seconds
300
As an object falls, ________ energy is converted to ________ energy.
Potential, Kinetic
400
A person pushes a box 4 meters across the floor. The force of friction on the box is 5 N. How much work did friction do on the box?
W=F*d
W=(-5)*4 = -20 J
400
A person pushes a block (mass = 5kg) with a force of 30 N. They push the block 10 meters in 5 seconds. Calulate the power of the person.
P=W/t
P=(F*d)/t
P=(30N * 10m) / 5s = 300/5 = 60W
400
A car (mass=1200kg) drives to the top of a 10 meter tall hill. At the top of the hill it has a speed of 13 m/s. What is the TOTAL energy of the car?
E(total) = KE + U
= 1/2mv^2 + mgh
= 219,000 J
400
Which boat is more efficient?
The bottom boat (less waste is created)
400
A rocket is shot striaght up with initally 25 J of kinetic energy. 3/4 of the way to its maximum height, it has this much kinetic energy: _____.
Energy is conserved (Etotal= KE +U)
Einitial = 25J (kinetic) + 0J (potential)
E3/4 up = (1/4)*25J (kinetic) + (3/4)*25J (potential) = 25 J
= 6.25J (kinetic) + 18.75J (potential)
500
A person applies lifts a 5kg object 3 meters off the gound. How much work does the person do on the object? (Fg=mg)
W=F*d
W=mg*d = 5*9.8*3 = 147 J
500
** Give a demonstration of completing a task with "low power" versus "high power" **
Same amount of work in less time = More power
or
More work in the same amount of time = More power
500
A car (mass 1200kg) has 100,000 J of kinetic energy. What is the velocity of the car? (Solve for v)
KE=1/2mv^2
100,000 = (1/2)(1200)(v2)
166.67 = v2
v=12.9 m/s
500
A machine that is 20% efficient requires an input energy of 100 J. What is the output energy of this machine?
20%=(output/100)*100
0.2 = output/100
output = 20 J
500
A 6 kg block (initially at rest) is pushed horizontally by a force of 10 N. What is the speed of the block after being pushed 5 meters?
4.08 m/s