How Many Beers Does It Take to Reimburse Energy Expenditure?

In summary, the problem involves a sled being pulled by a force at an angle on a horizontal road with a coefficient of kinetic friction. To find the energy dissipated by friction, the formula used is delta E thermal = F * delta x, where F is the kinetic friction force and delta x is the distance the sled is pulled. However, the normal force is not equal to the force of gravity because there is another force acting in the vertical direction. The correct approach would be to subtract the force applied at the 30 degree angle from the force of gravity and use that value for the normal force in the formula.
  • #1
nns91
301
1

Homework Statement



A man lifted a full keg of beer (mas 62kg) to a height of about 2m 676 times in 6 hours. Assuming that work was done only as the keg was going up, estimate how many such kegs of beer he would have to drink to reimburse his energy expenditure. (1 L of beer is approximately 1kg and provides about 1.5MJ of energy; in calculation neglect the mass of the empty keg)

Homework Equations



W=[tex]\Delta[/tex]K

The Attempt at a Solution



So E= F.[tex]\Delta[/tex]x =mgx= 62*9.81*2

For 676 times E=672*62*9.81*2[tex]\approx[/tex] 822313 J.

So the energy he needs to take in is 822313 J which is smaller than 1.5MJ so it means he will need less than 1 L of beer ??

Am I wrong ?
 
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  • #2
I think you made it right even if you wrote "672" instead of 676 in
For 676 times E=672*62*9.81*2LaTeX Code: \\approx 822313 J.
 
  • #3
Amusing problem by the way. I think that you did it right, I got that it was 0.5482 L or 0.008842 kegs of beer.
 
  • #4
My bad. So my approach is right ??

One more problem:

So I am given a 8kg sled is initially at rest on a horizontal road. The coefficient of kinetic friction between the sled an the road is 0.4. The sled is pulled a distanced of 3m by a force of 40 N applied to the sled at an angle of 30 degree.

They ask for the energy dissipated by friction

So I have delta E thermal = F* delta x= 0.4*8*9.81*3

However I got the wrong answer. Is my approach right ?
 
  • #5
The normal force is not equal to the force of gravity because there is another force acting in the vertical direction---the force being applied to the sled at the 30 degree angle.
 
  • #6
so will normal force equal force of gravity + Fsin30 ?
 
  • #7
Actually, subtract I meant. Anyway, I got it. THanks guys.
 

FAQ: How Many Beers Does It Take to Reimburse Energy Expenditure?

What is conservation of energy?

The law of conservation of energy states that energy cannot be created or destroyed, but can only be transferred or transformed from one form to another. This means that the total amount of energy in a closed system remains constant over time.

Why is conservation of energy important?

Conservation of energy is important because it is a fundamental principle of physics that helps us understand and predict the behavior of systems. It also allows us to make efficient use of energy resources and reduce waste and environmental impacts.

How is energy conserved?

Energy is conserved through various processes such as mechanical work, heat transfer, and chemical reactions. In any system, the total energy remains constant even if there are changes in the forms of energy present.

Are there any exceptions to the law of conservation of energy?

There are no known exceptions to the law of conservation of energy in classical physics. However, in quantum mechanics, there are some phenomena that appear to violate this law, but these are still being studied and understood.

How does conservation of energy relate to renewable energy sources?

Renewable energy sources, such as solar and wind power, also follow the law of conservation of energy. These sources convert energy from one form to another, but the total amount of energy remains constant. By using renewable energy sources, we can reduce our reliance on non-renewable sources and contribute to the conservation of energy resources.

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