Physics Help Forum Energy changes

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 Jul 1st 2015, 08:32 PM #1 Junior Member   Join Date: Jul 2015 Posts: 3 Energy changes a. If a bird is flying straight and level at a steady speed, what energy changes are taking place? b. And what energy changes are taking place when a bird dives down to catch a fish from a lake?
Jul 1st 2015, 11:29 PM   #2
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 Originally Posted by lilbexz a. If a bird is flying straight and level at a steady speed, what energy changes are taking place? b. And what energy changes are taking place when a bird dives down to catch a fish from a lake?
 The Helpers and the staff of the forum have agreed that they won't give a full answer to a problem posted with no attempt (except maybe in some cases). The Helpers are here to help you to understand your weaknesses by going through the asked questions with you and not here to solve your physics problems. It is imperative to show an attempt to a problem. If you don't know how to start, say it. Helpers will give you a push in the right direction.
What do you think the answers are? Where did you get these questions from? Are they part of your homework? We won't do your homework for you nor will you be able to find any other forum that will either. All forums have this rule.

 Jul 2nd 2015, 01:17 AM #3 Junior Member   Join Date: Jul 2015 Posts: 3 It is just a wee question that I have in my workbook, I am trying to understand it before I do my essay. I think a. is kinetic energy and b. potential energy into kinetic energy
Jul 2nd 2015, 01:36 AM   #4
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 Originally Posted by lilbexz It is just a wee question that I have in my workbook, I am trying to understand it before I do my essay. I think a. is kinetic energy and b. potential energy into kinetic energy
Excellent. Now explain why you think that's true.

 Jul 2nd 2015, 03:16 AM #5 Senior Member   Join Date: Apr 2015 Location: Somerset, England Posts: 708 Hint Note that the questions ask about energy changes, not directly about energy.
Jul 2nd 2015, 03:32 AM   #6
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 Originally Posted by studiot Hint Note that the questions ask about energy changes, not directly about energy.
Since he said its just energy I took it to mean there's no change as opposed to the way he expressed his second response where it was explicit so he and I are on the same wave length.

 Jul 2nd 2015, 04:08 AM #7 Senior Member   Join Date: Apr 2015 Location: Somerset, England Posts: 708 The original question is rather vague so it is diffcult to know what is required without further discussion from the OP.
Jul 2nd 2015, 04:40 AM   #8
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 Originally Posted by studiot The original question is rather vague so it is diffcult to know what is required without further discussion from the OP.
On the contrary. The OP was very clear

Question a: If a bird is flying straight and level at a steady speed, what energy changes are taking place?

Answer b. Since the speed is steady then the kinetic energy is constant. Since the flight is level then the gravitational potential energy is also constant. Therefore the total energy, being the sum of the two, is also constant.

Question b. And what energy changes are taking place when a bird dives down to catch a fish from a lake?

Answer b. When a bird dives down its speed increases and so its kinetic energy increases. Since its moving down its potential energy decreases. Those are the only changes that we know happen. If we knew how the speed of the bird changes with height then would could determine if the total energy is constant. But since all we know is that the bird dives down we have no knowledge about its speed. We can only assume that it increases as its height decreases.

So your claim that the question is "rather vague" is clearly wrong, i.e. its quite clear.

 Jul 2nd 2015, 06:11 AM #9 Senior Member   Join Date: Apr 2015 Location: Somerset, England Posts: 708 I find it is usually best to ask what someone means (ask for clarification) rather than challenge them. I am quite comfortable with my statement.
Jul 6th 2015, 07:01 PM   #10
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 Originally Posted by studiot I find it is usually best to ask what someone means (ask for clarification) rather than challenge them.
I don't get it. What exactly are you talking about? What about the question original has you so confused? And what about his answer has you confused. The only one who made a mistake here was me. Not the person who created the question and not the poster. I mistook question "a" as being correct for some odd reason.

I don't know why I missed that. Well ... nobody's perfect.

But while you might be happy with what you wrote that doesn't mean you haven't been posting confusing comments such as assertions that the question was vague when it was very clear.

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