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Need help with finding thermal and Kinetic energy

  • Thread starter Sherlock01
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  • #1
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Homework Statement


A block starts at rest. A hand pushes the block with 6.1 N to the right across a rough surface, with 1.5 N of friction. if the block moves 1.6 m horizontally determine the following (a) work done by hand (b) work done by friction (c) the amount of thermal energy created (d) the amount of kinetic energy created?

Homework Equations


W= F x D
work by force = F x D

The Attempt at a Solution


6.1 x 1.6 = 9.76
1.5 x 1.6 = -2.4[/B]
 

Answers and Replies

  • #3
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Per forum rules, you must show some attempt.
i added what i have so far can u help me solve the rest please
 
  • #5
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What do you think the two things you added represent?
the 2 things i added are the answers to the first two parts of the question for what is the work done by friction and just work done overall
 
  • #6
haruspex
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Further to PeterDonis' question:
Always show units and make it clear which question you are answering and what you are calculating.
The second equation you added is clearly wrong because you left something out on the left hand side.
 
  • #7
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Further to PeterDonis' question:
Always show units and make it clear which question you are answering and what you are calculating.
The second equation you added is clearly wrong because you left something out on the left hand side.
um i know that the answer is right because this is on a web assign that my teacher assigned i understand i left the negatives out but i just add the negative in to the final answer rather than thinking about the negative prior to that
 
  • #8
haruspex
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work done overall
You mean, work done by the hand. It is not clear what "work done overall" would mean.

So how about c)? Where does the thermal energy come from?
 
  • #9
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um i know that the answer is right because this is on a web assign that my teacher assigned i understand i left the negatives out but i just add the negative in to the final answer rather than thinking about the negative prior to that
however i would like assistance with the second half of the problem that would be awesome because that is the only part im confused on
 
  • #10
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however i would like assistance with the second half of the problem that would be awesome because that is the only part im confused on
ahhh oh yes that was my bad sry
 
  • #11
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ahhh oh yes that was my bad sry
well i know thermal energy is based off of the friction
 
  • #12
haruspex
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um i know that the answer is right because this is on a web assign that my teacher assigned i understand i left the negatives out but i just add the negative in to the final answer rather than thinking about the negative prior to that
It is worth being more rigorous. It might not always be obvious what the sign of the answer should be.
The minus sign on the right should result from one on the left. Why should there be a minus sign on the left?
well i know thermal energy is based off of the friction
Right, so what does that imply for the answer to c?
 
  • #13
haruspex
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ahhh oh yes that was my bad sry
This is rather confusing. You seem to be clicking on the wrong Reply buttons, so you end up "replying" to one of your own posts instead of the one you are really responding to.
 
  • #14
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This is rather confusing. You seem to be clicking on the wrong Reply buttons, so you end up "replying" to one of your own posts instead of the one you are really responding to.
sorry i figured out C tho i realized that its relative to friction work done the answer is 2.4
 
  • #15
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now were on to d) which im still confused i would usually do 1/2 x m x v^2
 
  • #16
haruspex
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sorry i figured out C tho i realized that its relative to friction work done the answer is 2.4
That leaves d). Any thoughts?
 
  • #17
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however in this problem i do not have a mass to use
 
  • #18
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That leaves d). Any thoughts?
well it probably has something to do with that equation from before but it must have to do with distance and force
 
  • #19
haruspex
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on to d) which im still confused i would usually do 1/2 x m x v^2, however in this problem i do not have a mass to use
It is possible to do it that way - just introduce an unknown m for the mass and watch it disappear later when you simplify the equations.
But there is an easier way. Of the work done by the hand, what are all the places it can go?
 
  • #20
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It is possible to do it that way - just introduce an unknown m for the mass and watch it disappear later when you simplify the equations.
But there is an easier way. Of the work done by the hand, what are all the places it can go?
well the work done by the hand must become thermal energy because of the presence of friction so it must transfer into the surface its sliding accrossed
 
  • #21
haruspex
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well the work done by the hand must become thermal energy because of the presence of friction so it must transfer into the surface its sliding accrossed
You have calculated the work done by the hand and the work done by friction, and they do not add to zero. Where has the rest gone?
 

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