sarah99630
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http://pmt.physicsandmathstutor.com/...0&%20Power.pdf
please check that question out,it's part of question 28. Can someone please explain why they said in the answer "mention of kinetic energy loses the mark" huh? I thought generally when something descends GPE is converted to K.E and not 100% efficient sure..but in this case theyre talking about the WHOLE GPE (I literally had previously calculated the lost GPE they asked for using mgh)
please help..thanks
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sarah99630
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in the same question,28, how do I find the last part? and why? Thanks
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Pangol
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(Original post by sarah99630)
http://pmt.physicsandmathstutor.com/...0&%20Power.pdf
please check that question out,it's part of question 28. Can someone please explain why they said in the answer "mention of kinetic energy loses the mark" huh? I thought generally when something descends GPE is converted to K.E and not 100% efficient sure..but in this case theyre talking about the WHOLE GPE (I literally had previously calculated the lost GPE they asked for using mgh)
please help..thanks
The question says that the cyclist is moving at a constant velocity, so there cannot be any increase in KE. That GPE must be going somewhere else!

Think what if feels like when you are cycling along at speed. Is there any force that you feel that might be trying to slow you down? How can this be overcome? Remember also that work done and energy transferred are effectively the same thing.
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sarah99630
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(Original post by Pangol)
The question says that the cyclist is moving at a constant velocity, so there cannot be any increase in KE. That GPE must be going somewhere else!

Think what if feels like when you are cycling along at speed. Is there any force that you feel that might be trying to slow you down? How can this be overcome? Remember also that work done and energy transferred are effectively the same thing.
Ohh so that's why!!! Thank you so much!So when something is being converted to kinetic energy there must be an acceleration? Oh so theyre basically asking why he is not accelerating if gravity is acting on him?
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Pangol
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(Original post by sarah99630)
Ohh so that's why!!! Thank you so much!So when something is being converted to kinetic energy there must be an acceleration? Oh so theyre basically asking why he is not accelerating if gravity is acting on him?
Assuming the mass of the object stays constant (and you're unlikely to meet many questions where this is not the case, although they do occur), the only way that the KE can change is if the speed changes - so yes, there must be some acceleration. Think about dropping a stone from a tall building - this is the sort of situation where GPE gets converted into KE. But now think about the same situation where the stone falls for a very long time. Does it continue to get faster and faster and faster? Or does something else happen? That is a similar situation to what is going on here.
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sarah99630
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(Original post by Pangol)
Assuming the mass of the object stays constant (and you're unlikely to meet many questions where this is not the case, although they do occur), the only way that the KE can change is if the speed changes - so yes, there must be some acceleration. Think about dropping a stone from a tall building - this is the sort of situation where GPE gets converted into KE. But now think about the same situation where the stone falls for a very long time. Does it continue to get faster and faster and faster? Or does something else happen? That is a similar situation to what is going on here.
yess I get it perfectly now! thanks A LOT.
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