Energy conversation and friction

In summary, energy conservation refers to the practice of reducing energy consumption to preserve natural resources and minimize environmental impact. Friction can negatively affect energy conservation by converting energy into heat. Some examples of energy conservation in daily life include turning off lights and using public transportation. To reduce friction and improve energy conservation, lubricants and smoother materials can be used. Energy conservation is important for reducing dependence on non-renewable resources, combating climate change, and saving money.
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Homework Statement


At a construction site, a 65 kg bucket of concrete hangs from a light (but strong) cable that passes over a light friction-free pulley and is connected to an 80.0 kg box on a horizontal roof. The cable pulls horizontally on the box, and a 50.0 kg bag of gravel rests on top of the box. The coefficients of friction between the box and roof are shown.

A. Find the friction force on the bag of gravel and on the box.
B. Suddenly a worker picks up the bag of gravel. Use the energy conservation to find the speed of the bucket after it has descended 2.0 m from rest.

http://img237.imageshack.us/img237/8178/yf0729.jpg

Homework Equations



Ki + Ui + Wdissipative = Kf + Uf

The Attempt at a Solution



The frictional force on the gravel is 0 because it's not on the ground. For the box it's (130 kg)(9.8 m/s2)(0.7) = 891.8N.

Initial kinetic energy: 0
Initial gravitation potential energy: (65 kg)(9.8 m/s2)(2.0 m) = 1274 J
Dissipative work: (80.0 kg)(9.8 m/s2)(0.4)(2.0 m) = 627.7 J
Final kinetic energy: ?
Final gravitational potential energy: 0

Ki + Ui + Wdissipative = Kf + Uf
0 + 1274J + 627.7J = Kf + 0
Kf = 1901.7 J
1901 J = (145 kg*v2)/2 ==> v = 5.12 m/s

Where did I go wrong? By the kinematics equations, it should be 2.99 m/s.
 
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  • #2
The two coefficents of friction are for standing and kinetic I hope.

only mistake i see is the "Ki + Ui + Wdissipative = Kf + Uf" If it is disspated it is on the right side.

Edited...
 
  • #3
Lok said:
The two coefficents of friction are for standing and kinetic I hope.

only mistake i see is the "Ki + Ui + Wdissipative = Kf + Uf" If it is disspated it is on the right side.

Edited...

Yes, that's it. I guess I copied that equation down incorrect. Thank you very much. :smile:

Here are the corrected calculations for anyone else with this problem:

Ki + Ui = Kf + Uf + Wdissipative
0 + 1274J = Kf + 0 + 627.7J
Kf = 646.3J
646.3J = (145 kg*v2)/2 ==> v = 2.99 m/s
 

1. What is energy conservation?

Energy conservation refers to the practice of reducing energy consumption in order to preserve natural resources and minimize environmental impact. This can include measures such as using renewable energy sources, improving energy efficiency, and reducing waste.

2. How does friction affect energy conservation?

Friction is a force that opposes motion, and it can cause energy to be lost as heat. This means that when objects rub against each other, some of the energy that was used to move them is converted into heat energy. This can have a negative impact on energy conservation, as it means more energy is needed to achieve the same result.

3. What are some examples of energy conservation in daily life?

There are many ways to practice energy conservation in daily life, such as turning off lights and electronics when not in use, using public transportation or carpooling instead of driving alone, and choosing energy-efficient appliances and light bulbs. Other examples include using natural lighting and ventilation, and recycling and reducing waste to conserve resources.

4. How can we reduce friction to improve energy conservation?

One way to reduce friction is by using lubricants, such as oil or grease, to create a barrier between moving surfaces. This can help to minimize the amount of energy that is lost as heat. Another way is by using smoother materials or surfaces that have less resistance to motion.

5. Why is energy conservation important?

Energy conservation is important for several reasons. It helps to reduce our dependence on non-renewable resources, which are finite and can have harmful effects on the environment. It also helps to reduce greenhouse gas emissions and combat climate change. Additionally, energy conservation can save individuals and businesses money on energy bills and promote sustainable living practices.

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