Thermodynamics weightlifter

In summary, a weight lifter who lifts a 147 kg weight a distance of 1.1 m and treats herself as a thermodynamic system must put out -2035.34 J of heat if her internal energy decreases by 3620 J. The units of Q are in joules and can be converted to kcal by multiplying by approximately 4184.
  • #1
chukie
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Homework Statement


A weight lifter manages to lift a 147 kg weight a distance of 1.1 m. Treat her as a thermodynamic system and find how much heat (in kcal) she must put out if her internal energy decreases by 3620 J during the lift.


Homework Equations



delta U=Q-W

The Attempt at a Solution



-3620= Q-(9.8*147*1.1)
Q=-2035.34

I was wondering wut the units of Q are? if it's in joules how do i convert to kcal?

Thanks in advance!:smile:
 
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  • #2
Q is in Joules because you have used consistent metric units.
A kCal is approx 4184J - it's the energy need to heat 1cc of water 1deg C.
 
  • #3


I would like to first clarify that a weight lifter cannot be treated as a thermodynamic system as they are a biological organism and not an idealized system. However, we can use the principles of thermodynamics to calculate the amount of heat that the weight lifter must put out during the lift.

Using the equation delta U = Q - W, we can rearrange to solve for Q:

Q = delta U + W

We are given delta U = -3620 J and W = 9.8 * 147 * 1.1 = 1614.06 J. Plugging these values in, we get:

Q = -3620 J + 1614.06 J = -2005.94 J

The units of Q are in joules, as heat is a form of energy and energy is measured in joules. To convert to kcal, we can use the conversion factor 1 J = 0.000239 kcal. Therefore, the weight lifter must put out:

Q = -2005.94 J * (0.000239 kcal/J) = -0.479 kcal

This means that the weight lifter must output 0.479 kcal of heat during the lift to decrease her internal energy by 3620 J. It is important to note that this is a simplified calculation and does not take into account other factors such as the body's metabolism and energy production during the lift.
 

1. How does a thermodynamics weightlifter work?

A thermodynamics weightlifter uses principles of thermodynamics, specifically the second law of thermodynamics, to convert heat energy into mechanical energy. This is done through the use of a heat engine, which converts thermal energy into mechanical work.

2. What makes a thermodynamics weightlifter different from a regular weightlifter?

A thermodynamics weightlifter differs from a regular weightlifter in that it does not rely on muscular strength to lift weights. Instead, it utilizes the principles of thermodynamics to generate the necessary energy for lifting.

3. Can a thermodynamics weightlifter lift heavier weights than a regular weightlifter?

In theory, yes. Since a thermodynamics weightlifter does not rely on muscular strength, it can potentially lift heavier weights. However, in practice, the efficiency of heat engines is limited, so a thermodynamics weightlifter may not be able to lift significantly heavier weights than a regular weightlifter.

4. How does the second law of thermodynamics apply to a thermodynamics weightlifter?

The second law of thermodynamics states that in any energy conversion, some energy will be lost as heat. In the case of a thermodynamics weightlifter, some of the heat energy used to power the lifting motion will be lost as heat, which cannot be converted back into mechanical energy.

5. Can a thermodynamics weightlifter be used for practical applications?

Yes, thermodynamics weightlifters have been used in various applications, such as powering generators or pumps in remote areas where electricity is not readily available. They can also potentially be used in space exploration, where traditional weightlifting methods are not feasible.

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