Calculating Energy and Friction in a Child's Descent on a 6m Slide

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Homework Help Overview

The discussion revolves around calculating energy and friction related to a child's descent on a slide, specifically focusing on energy transformations and the impact of friction during the descent. The problem involves concepts from mechanics, particularly potential and kinetic energy, as well as frictional forces.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between potential energy at the top of the slide and kinetic energy at the bottom, questioning how to account for energy lost to friction. There are attempts to clarify the definitions of work and energy in this context, with some participants expressing confusion about the calculations and the components of the slide.

Discussion Status

The discussion is active, with participants sharing their calculations and questioning the assumptions made about energy conservation and the role of friction. Some guidance has been offered regarding the need to compare energies at the top and bottom of the slide, but there is no explicit consensus on the interpretation of the results or the calculations involved.

Contextual Notes

Participants are working under the constraints of a homework problem, which may limit the information available for solving the questions. There is an ongoing debate about the definitions of energy "used" versus "wasted" in the context of overcoming friction.

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A child of mass 26kg is traveling at 4.0ms at the bottom of the slide which is 2m vertically below the top. The length of the slide is 6m.
Calculate

i) The energy used in overcoming the friction during the child's descent

ii) The magnitude of the frictional force.

Totally confused about this question. I know Work done = Force.displacement in the direction of the force but then does this mean that question i) is equal to W=26(9.8)Cos19.47?

I have no idea. Would appreciate any help.

thank you
 
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Assume the child started at the top with zero speed. What's the total energy at the top? At the bottom?
 
At the top would be the potential energy so 26*9.8*2, but this would be the energy output (I think). That's not really what i) is asking. At the bottom would also be the same but in kinetic energy form.
 
ZAMM said:
At the bottom would also be the same but in kinetic energy form.
Why don't you check and see? They give you the speed. (The energy would only be the same if there were no losses to friction.)
 
OK, so at the bottom of the slide E=.5(26)(4)^2 but I'm still confused. The length of the slide has 2 components? is the horizontal component the frictional component? I have no clue.
 
Potential energy only deals with vertical displacement. You need the length of the slide for the second part of the question
 
I know it only deals with vertical displacement but in this context the energy that requires him to get from the top to the bottom (neglecting the slide) would be mgh, but this alone does not help me solve the equation.
 
ZAMM said:
OK, so at the bottom of the slide E=.5(26)(4)^2 but I'm still confused.
Good. How does that compare to the energy it started with at the top?
 
The problem deals with conservation of energy. Etop=Ebottom. Without friction, PEtop=KEbottom, but that's not what you have here.
 
  • #10
At the top PE=mgh=26*9.8*2=509.6J and at the bottom KE=.5*26*4^2=208J. Energy is greater at the top than at the bottom.
 
  • #11
OK, so what's the answer to the first question?
 
  • #12
The difference between them? but if it is that, what I calculated is not energy "used" but more wasted.
 
  • #13
ZAMM said:
The difference between them? but if it is that, what I calculated is not energy "used" but more wasted.
That depends on your point of view: You "used" it to overcome friction.
 

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