Help with change in internal energy for a real system.

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Homework Help Overview

The problem involves Tarzan's fall from a height and the subsequent change in internal energy as he transitions from a free fall to a crouched position. The subject area includes concepts of energy, specifically kinetic and potential energy, in the context of a real system versus an idealized point particle system.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • Participants discuss the need to consider both kinetic and potential energy for the change in internal energy. There is uncertainty about how to calculate kinetic energy in the context of a real system compared to a point particle system.

Discussion Status

Some participants have provided insights into the types of energy involved, while others express confusion regarding the calculations needed for the real system. There is an ongoing exploration of how to approach the problem without reaching a definitive conclusion.

Contextual Notes

Participants note the distinction between the point particle system and the real system, indicating that assumptions about energy conservation may differ. There is also mention of the specific heights and masses involved, which may influence the calculations.

guitarguy1
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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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Not 100% sure, but I think you just consider the kinetic and potential energy.
 
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.
 
The velocity of the center-of-mass would be used for either the point particle or the real system.
 

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