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Potential energy of a block moving up and down an incline.

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Homework Statement


Which graphy represents the potential energy of the block as a function of time?

Homework Equations


PE=mgh

The Attempt at a Solution


First, the potential energy is zero until it reache the top of the incline where the potential energy is maximum. Moving down, the potential energy decreases until zero. But then I am confused is it a parabolic graph like D or linear?
 

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  • #2
kuruman
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Homework Statement


Which graphy represents the potential energy of the block as a function of time?

Homework Equations


PE=mgh

The Attempt at a Solution


First, the potential energy is zero until it reache the top of the incline where the potential energy is maximum. Moving down, the potential energy decreases until zero. But then I am confused is it a parabolic graph like D or linear?
To answer that question, you need to find U(t). Can you do that? Hint: h(t) will do because U(t) = mgh(t).
 
  • #3
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To answer that question, you need to find U(t). Can you do that? Hint: h(t) will do because U(t) = mgh(t).
Ahh, right the height is proportional to the time squared. So, it’s a parabola.
 
  • #4
kuruman
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Parabola is correct, but which one of the two shown?
 
  • #5
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D. Since it starts and ends with zero.
 
  • #6
kuruman
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D. Since it starts and ends with zero.
Not a good enough explanation. The zero value for potential energy is (as you know) arbitrary. What if the other graph was labeled so that the potential energy is zero at its end points?
 
  • #7
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Not a good enough explanation. The zero value for potential energy is (as you know) arbitrary. What if the other graph was labeled so that the potential energy is zero at its end points?
No, it starts with zero, reaches maximum height/ potential energy, and then decrease to zero.
 
  • #8
kuruman
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Right. The potential energy must exhibit a maximum and must be parabolic.
 

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