Internal Energy and kinetic friction

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Homework Help Overview

The discussion revolves around a physics problem involving internal energy and kinetic friction. The scenario describes a block being dragged over a rough surface, with a focus on calculating the increase in internal energy due to friction.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster expresses uncertainty about how to approach the problem, particularly regarding the concept of internal energy. Some participants discuss the relationship between frictional force and work done, while others emphasize the need to correctly identify the normal force acting on the block.

Discussion Status

The discussion is ongoing, with participants exploring different interpretations of the forces involved. Guidance has been provided regarding the calculation of the normal force, indicating a productive direction in the conversation.

Contextual Notes

There is a mention of the block not accelerating vertically, suggesting that the vertical forces must balance, which is a key assumption in the problem setup.

hats_06
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Homework Statement



Please help, I've been struggling with this question for so long! We haven't done internal energy so I am not sure even where to really begin?

A 10.0 kg block is dragged over a rough, horizontal surface by a 76.0 N force acting at 20.0° above the horizontal. The block is displaced 3.50 m, and the coefficient of kinetic friction is 0.300.

What is increase in internal energy of the block-surface system due to friction?
 
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The change in internal energy equals the work done against friction.
 
so if Ff= Uk.N...Then since Uk = 0.3 and N = 76.sin 20
So Ff = 7.8, Hence W = 7.8 x 3.5 = 27.3? I tried that answer but it didnt work :S
 
hats_06 said:
so if Ff= Uk.N...Then since Uk = 0.3 and N = 76.sin 20
First you must correctly solve for the normal force. 76sin20 is the vertical component of the applied force, not the normal force.

To find the normal force, analyze all the vertical forces that act on the block. Since the block doesn't accelerate vertically, vertical forces must sum to zero. Hint: There are three forces acting on the block that have vertical components; the normal force is one of them.
 

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