Original post by Teenie2
It doesn't matter which way round you write it you still get the same answer.
gain in KE- loss in GPE = 0 so v^2 - 196 = 0 so v^ = 196 so v = 14 m/s
OR
loss in GPE - gain in KE = 0 so 196 - v^2 = 0 so 196 = v^2 so v = 14 m/s
gain in KE- loss in GPE = 0 so v^2 - 196 = 0 so v^ = 196 so v = 14 m/s
OR
loss in GPE - gain in KE = 0 so 196 - v^2 = 0 so 196 = v^2 so v = 14 m/s
Yes, but in this question then here, why is it GPE - KE. It won't be the same answer in this question.
Original post by Reda2
In the image attached, why is the change in total energy KE - GPE, and not GPE - KE, and in what case would it be GPE - KE.
If someone can please explain this to me it would be great, thanks.
If someone can please explain this to me it would be great, thanks.
Can you post the whole question and the full working?
Original post by notnek
Can you post the whole question and the full working?
This for example, attached. You can see it is, Loss in KE - gain in GPE = work done against friction.
Why is it that, and why is it not, gain in GPE - KE = work done against friction?
Is it because it is going from KE to GPE?
Thanks
(edited 7 years ago)
Original post by Reda2
This for example, attached. You can see it is, Loss in KE - gain in GPE = work done against friction.
Why is it that, and why is it not, gain in GPE - KE = work done against friction?
Is it because it is going from KE to GPE?
Thanks
Why is it that, and why is it not, gain in GPE - KE = work done against friction?
Is it because it is going from KE to GPE?
Thanks
Referring to the image from your first post:
That's the solution but you haven't posted the question. Is the working on the left related to the working on the right?
Please post everything.
It's confusing since they talk about "work done against friction" but it seems to be equal to 0. I'd need to see the question before I can help you.
Original post by notnek
Referring to the image from your first post:
That's the solution but you haven't posted the question. Is the working on the left related to the working on the right?
Please post everything.
It's confusing since they talk about "work done against friction" but it seems to be equal to 0. I'd need to see the question before I can help you.
That's the solution but you haven't posted the question. Is the working on the left related to the working on the right?
Please post everything.
It's confusing since they talk about "work done against friction" but it seems to be equal to 0. I'd need to see the question before I can help you.
Sorry I forgot to attach them. The question in this reply.
Attachment not found
Original post by Reda2
Sorry I forgot to attach them. The question in this reply.
Attachment not found
I thought your issue was with the working that you posted in your original post.
This is a different question.
Can you please start again, and post the question and working that confused you and tell us again why.
Original post by notnek
Referring to the image from your first post:
That's the solution but you haven't posted the question. Is the working on the left related to the working on the right?
Please post everything.
It's confusing since they talk about "work done against friction" but it seems to be equal to 0. I'd need to see the question before I can help you.
That's the solution but you haven't posted the question. Is the working on the left related to the working on the right?
Please post everything.
It's confusing since they talk about "work done against friction" but it seems to be equal to 0. I'd need to see the question before I can help you.
Always use this formula..
WORK DONE AGAINST RESISTANCE = LOSS IN ENERGY (KE OR GPE) - GAIN IN ENERGY (KE OR GPE)
Always do whatever energy is lost - whatever energy is gained
In both questions (GPE at start) + (KE at start) = (GPE at finish) + (KE at finish) + (work done)
In question 1 there is no loss in energy (e.g. no air resistance) this means that
(GPE at start) + (KE at start) = (GPE at finish) + (KE at finish) + (work done) so (mgh) + (0) =(0) + (0.5mv^2) + (0) so 2 * 9.8 * 10 = 0.5 * 2 * v^2 so v^2 = 196 so v = 14 m/s
In question 2 there is work done to overcome friction so this means that
(GPE at start) + (KE at start) = (GPE at finish) + (KE at finish) + (work done) so
(GPE at start) - (GPE at finish) + (KE at start) - (KE at finish) = (work done against friction) so
(GPE at start - GPE at finish) + (KE at start) - (KE at finish) = (work done against friction) so
(mgh) + (0.5 * m * initial velocity ^2) - (0.5 * m * final velocity ^2) = (work done against friction) so
(6 * 9.98 * 2) + (0.5 * 6 * 4) - (0.5 * 6 * v^2) = (0.25 * FN * 4)
There's a youtube video at https://www.youtube.com/watch?v=dj8Y1Pof9XU that explains this using an example of a block starting from rest sliding down a slope that might help you.
In question 1 there is no loss in energy (e.g. no air resistance) this means that
(GPE at start) + (KE at start) = (GPE at finish) + (KE at finish) + (work done) so (mgh) + (0) =(0) + (0.5mv^2) + (0) so 2 * 9.8 * 10 = 0.5 * 2 * v^2 so v^2 = 196 so v = 14 m/s
In question 2 there is work done to overcome friction so this means that
(GPE at start) + (KE at start) = (GPE at finish) + (KE at finish) + (work done) so
(GPE at start) - (GPE at finish) + (KE at start) - (KE at finish) = (work done against friction) so
(GPE at start - GPE at finish) + (KE at start) - (KE at finish) = (work done against friction) so
(mgh) + (0.5 * m * initial velocity ^2) - (0.5 * m * final velocity ^2) = (work done against friction) so
(6 * 9.98 * 2) + (0.5 * 6 * 4) - (0.5 * 6 * v^2) = (0.25 * FN * 4)
There's a youtube video at https://www.youtube.com/watch?v=dj8Y1Pof9XU that explains this using an example of a block starting from rest sliding down a slope that might help you.
Original post by fpmaniac
Always use this formula..
WORK DONE AGAINST RESISTANCE = LOSS IN ENERGY (KE OR GPE) - GAIN IN ENERGY (KE OR GPE)
Always do whatever energy is lost - whatever energy is gained
WORK DONE AGAINST RESISTANCE = LOSS IN ENERGY (KE OR GPE) - GAIN IN ENERGY (KE OR GPE)
Always do whatever energy is lost - whatever energy is gained
That's the answer I was looking for, thank you very much.
Quick Reply
Related discussions
- How Hard is A Level Further Maths?
- the issac physics astronomy question
- Edexcel IAL Maths & Further Mathematics
- Further Maths 2023/2024!!!
- IAL repeats cash in.
- Edexcel A-level Biology B Paper 2 (9BI0 02) - 16th June 2023 [Exam Chat]
- What units do I need for Edexcel IAL or IAS Further Maths
- GCSE Exam Discussions 2024
- Messed up CIE Math P3 and Physics P4.
- Revising for Edexcel's AS Maths - running out of material.
- A-level Physics Study Group 2022-2023
- Arsey's solutions
- Leeds Beckett University Software Engineering MEng A levels Access course
- GCSE Physics Question Help
- Anyone know where to find the 2023 AS Edexcel Further Maths papers?
- A level physics help
- Help in statistics please
- Deciding Edexcel IAL FM Cash-in Unit Combinations
- EDEXCEL A-LEVEL PSYCHOLOGY PAPER 3 (9PS 03) - 3rd June [Exam Chat]
- Grade Growth Chronicles | From C's to A's (23-24)
Latest
Trending
Last reply 2 days ago
Did Cambridge maths students find maths and further maths a level very easy?Last reply 2 weeks ago
Edexcel A Level Mathematics Paper 2 unofficial mark scheme correct me if wrongMaths
71
Trending
Last reply 2 days ago
Did Cambridge maths students find maths and further maths a level very easy?Last reply 2 weeks ago
Edexcel A Level Mathematics Paper 2 unofficial mark scheme correct me if wrongMaths
71
