Kinetic Energy
Gravitational Potential Energy
Conservation of Energy
(Must be Done in Order)
(Must be Done in Order)
Work
Energy Transfer
100
Calculate the Kinetic Energy of a 10 kg mass moving with a speed of 12 m/s.
KE = mass/2 x (speed)2
KE = 10kg/2 x (12 m/s)2
KE = 720 J
100
Calculate the Gravitational Potential Energy with a mass of 12 kg dropped from a height of 100 meters. (Use 10 m/s/s for gravity)
GPE = mass x gravity x height
GPE = 12 kg x 10 m/s/s x 100 m
GPE = 12,000 J
100
Calculate the Gravitational PE at point A and the KE if the starting speed is 0 m/s and the mass is 10 kg. (Use 10 m/s/s for g.)
GPE = mass x gravity x height
GPE = 10 kg x 10 m/s/s x 140 m
GPE = 14,000 J
KE = m/2 (speed)2
KE = 10 kg/ 2 (0 m/s)2 = 0 J
Keep the GPE and Mass for this problem on your whiteboards for later.
100
A pizza delivery person holds a pizza on his hands and walks forward towards a house to deliver the pizza. How much work was done?
No work is done because the direction of the force is up and the direction of travel is forward. Those directions are not parallel so no work is done.
100
A 0.25 kg bouncy ball is dropped from 1 meter. After striking the floor it rebounds to 0.57 meter. How much energy was transferred to heat and sound.
Work is change in energy.
W = PEf - PEi
W = (0.25kg)(9.8 m/s2)(0.57m) - (0.25kg)(9.8m/s2)(1m)
W = 1.39 J - 2.45 J = - 1.06 J Transferred
BONUS: If the same ball is dropped in vacuum chamber where there is no air, does the ball bounce as high? Why?
200
Calculate the Kinetic Energy of a 50 kg mass moving at 2 m/s.
KE = mass/2 x (speed)2
KE = 50kg/2 x (2 m/s)2
KE = 100 J
200
Calculate the Gravitational Potential Energy with a mass of 1000 kg dropped from a height of 10 meters. (Use 10 m/s/s for gravity)
GPE = mass x gravity x height
GPE = 1000 kg x 10 m/s/s x 10 m
GPE = 100,000 J
BONUS: When a person lifts a weight over their heads, they used this type of energy to do work on the weight to increase the GPE.
200
What is the KE & GPE at the bottom of the first hill between A & B?
GPE = mass x gravity x height
GPE = 10 kg x 10 m/s/s x 0 m
GPE = 0 J
By Conservation of Energy PEi = KEf
KE = 14,000 J
BONUS: If TME is not conserved, what two energies were produced? Hint: Think friction!
200
The same pizza delivery person lowers the pizza and hands it to the customer. Was work done?
Work was done because the direction of the force was up and direction of travel was down. Up and down are parallel to each other so work is done.
200
A 0.75 kg basketball is dropped downward from a height of 100 meters. The basketball rebounds 25 meters. How much work did the ground do on the basketball?
Work is change in energy.
W = PEf - PEi
W = (0.75kg)(9.8 m/s2)(25m) - (0.75kg)(9.8m/s2)(100m)
W = 183.75 J - 735 J = - 551.25 J Transferred
300
Calculate the Kinetic Energy of a 1000 kg mass moving with a speed of 0 m/s.
KE = mass/2 x (speed)2
KE = 1000kg/2 x (0 m/s)2
KE = 0 J
BONUS: When you add up KE, GPE and EPE in a system it is called this?
300
Calculate the Gravitational Potential Energy with a mass of 75 kg dropped from a height of 150 meters. (Use 10 m/s/s for gravity)
GPE = mass x gravity x height
GPE = 75 kg x 10 m/s/s x 150 m
GPE = 112,500 J
300
What is the KE & GPE at point B?
GPE = mass x gravity x height
GPE = 10 kg x 10 m/s/s x 95 m
GPE = 9,500 J
KE = TE - PEi
KE = 14,000 J - 9,500 J = 4,500 J
300
Calculate the work done when a 100 Newton rightward force is applied to an object to move it rightward 20 meters.
Work = force x distance
Work = 100 N x 20 m
Work = 2,000 J
300
A 1200 kg car traveling 35 m/s hits a large puddle of water and slows to 25 m/s. How much work did the puddle do on the car?
Work is change in energy.
W = KEf - KEi
W = (0.5)(1200kg)(25m/s)2 - (0.5)(1200kg)(35m/s)2
W = 375,000 J - 735,000 J = - 360,000 J Transferred
400
Calculate the speed of a 100 kg mass with a Kinetic Energy of 1200 J.
KE = mass/2 x (speed)2
(speed)2 = KE / (mass/2)
(speed)2 = 1200 J / 50 kg
speed = sqrt ((1200J) /(50kg)) = 4.9 m/s
400
Calculate the Gravitational Potential Energy with a mass of 20 kg dropped from a height of 170 meters. (Use 10 m/s/s for gravity)
GPE = mass x gravity x height
GPE = 20 kg x 10 m/s/s x 170 m
GPE = 34,000 J
400
What is the KE & GPE at point C?
GPE = mass x gravity x height
GPE = 10 kg x 10 m/s/s x 80 m
GPE = 8,000 J
KE = TE - PEi
KE = 14,000 J - 8,000 J = 6,000 J
400
Calculate the force that is applied when 10,000 Joules of work are done upward to lift it 30 meters downward.
Work = force x distance
Force = work / distance
Force = 10,000 J / -30 m
Force = 333.33 N
BONUS: Was this positive or negative work?
400
A 22 kg pendulum swings from a height of 10 meters. It swings back to a height of 8.8 meters. How much work did friction and air resistance do on the pendulum?
Work is change in energy.
W = PEf - PEi
W = (22kg)(9.8 m/s2)(8.8m) - (22kg)(9.8m/s2)(10m)
W = 1,897.28 J - 2156 J = - 258.72 J Transferred
500
This type of RENEWABLE energy captures the Kinetic Energy of moving air, changes it to Angular Kinetic Energy and produces Electrical Potential Energy.
Wind Energy
BONUS
This other source of RENEWABLE Energy is the sole cause of the Wind Energy and can be captured with photovoltaics.
500
These types of NONRENEWABLE Energy sources use stored Chemical Potential Energy, changes to Thermal Energy and finally into Electrical Potential Energy.
Coal, Oil, Natural Gas
BONUS: What are these nonrenewable energy sources called?
500
This RENEWABLE Energy source transfers Gravitational Potential Energy into Kinetic Energy into Rotational Kinetic Energy into Electrical Potential Energy. It also requires consideration of the local aquatic wildlife.
Hydroelectric Energy
500
This type of NONRENEWABLE Energy harnesses the energy inside of a nucleus, transfers that into Thermal Energy, then to Angular Kinetic Energy and finally into Electrical Potential Energy.
Nuclear Fission Energy
500
This type of RENEWABLE Energy harnesses Thermal Energy, transfers it to Angular Kinetic Energy and then to Electrical Potential Energy.
Geothermal Energy