Help with change in internal energy for a real system.

In summary, Tarzan, with a mass of 110 kg, falls from a tree limb where his center of mass is at a height of 3.0 m above the ground and the bottom of his feet are at a height of 2.0 m. Just before hitting the ground, he has dropped 2.0 m and his center of mass is now at a height of 1.0 m. Upon hitting the ground, his knees bend and he ends up in a crouched position with his center of mass 0.5 m above the ground. The speed at the instant just before his feet touch the ground is 6.261 m/s. The net change in internal energy for Tarzan from just before
  • #1
guitarguy1
14
0

Homework Statement



Tarzan, whose mass is 110 kg, is hanging at rest from a tree limb. Then he let's go and falls to the ground. Just before he let's go, his center of mass is at a height 3.0 m above the ground and the bottom of his dangling feet are at a height 2.0 above the ground. When he first hits the ground he has dropped a distance 2.0, so his center of mass is (3.0 - 2.0) above the ground. Then his knees bend and he ends up at rest in a crouched position with his center of mass a height 0.5 above the ground.
(a) Consider the point particle system. What is the speed v at the instant just before Tarzan's feet touch the ground?
(b) Consider the real system. What is the net change in internal energy for Tarzan from just before his feet touch to the ground to when he is in the crouched position?

Homework Equations



Fnet x distance = 1/2mv^2

The Attempt at a Solution



Part (a) was easy. I got 6.261 m/s. I'm having trouble with part (b). I at first thought it might be 0 J since it asks to consider the real system rather than point particle system, but that's not right. I understand that its just the energy exerted to bring him to a stop, but I'm not really sure what to do here.
 
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  • #2
Not 100% sure, but I think you just consider the kinetic and potential energy.
 
  • #3
Redbelly98 said:
Not 100% sure, but I think you just consider the kinetic and potential energy.

alright. But, I'm having trouble calculating the kinetic energy since this is for a real system whereas the other value i calculated was the velocity for the point-particle system.
 
  • #4
The velocity of the center-of-mass would be used for either the point particle or the real system.
 

1. How is internal energy defined in a real system?

Internal energy in a real system is the sum of the kinetic and potential energies of all the particles within the system. It also includes the energy associated with their interactions, such as chemical bonds or forces between molecules.

2. What causes a change in internal energy for a real system?

The change in internal energy for a real system can be caused by various factors, such as changes in temperature, pressure, or volume. It can also be affected by chemical reactions, phase transitions, or energy transfer to or from the system.

3. How is the change in internal energy calculated for a real system?

The change in internal energy for a real system can be calculated using the equation ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat transferred to the system, and W is the work done by the system.

4. How does the first law of thermodynamics relate to changes in internal energy for a real system?

The first law of thermodynamics states that the change in internal energy of a closed system is equal to the heat transferred to the system minus the work done by the system. This means that any changes in internal energy must be balanced by an equal amount of energy entering or leaving the system.

5. What factors can affect the accuracy of calculating changes in internal energy for a real system?

There are several factors that can affect the accuracy of calculating changes in internal energy for a real system, such as neglecting energy transfer through radiation, assuming ideal conditions, or not accounting for all energy forms within the system. Also, experimental errors and uncertainties can contribute to inaccuracies in the calculated change in internal energy.

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