Wahi_B
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What is substitution?
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Notnek
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(Original post by Wahi_B)
What is substitution?
Please give more context.
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bambi1425
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generally when something takes the place of another
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Wahi_B
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I'm not sure if this question requires it but I think it might.

A motorbike has a mass of 300kg that is being ridden along a straight road.
The rider sees a traffic queue ahead and reduces the speed of the motorbike from 18 m/s to 3 m/s.

How much work is done on the motorbike by the braking force?
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bambi1425
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I think you just need the right work done equation?? honestly not sure though, haven't looked at one of these for a while. apologies.
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Notnek
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(Original post by Wahi_B)
I'm not sure if this question requires it but I think it might.

A motorbike has a mass of 300kg that is being ridden along a straight road.
The rider sees a traffic queue ahead and reduces the speed of the motorbike from 18 m/s to 3 m/s.

How much work is done on the motorbike by the braking force?
I’m not sure what you mean by “substitution” in this context. You need to find the decrease in kinetic energy and that’s equal to the work done by the breaking force. Are you able to do that?
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Wahi_B
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(Original post by bambi1425)
I think you just need the right work done equation?? honestly not sure though, haven't looked at one of these for a while. apologies.
It's ok haha. I know the answer but I don't know how I got there
Apparently, it's 1/2 x 300kg x 3 m/s
But where does the half come from????
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Wahi_B
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(Original post by Sir Cumference)
I’m not sure what you mean by “substitution” in this context. You need to find the decrease in kinetic energy and that’s equal to the work done by the breaking force. Are you able to do that?
I have absolutely no idea how to do that

Wait never mind I think I have done it. Thanks anyways.
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Notnek
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(Original post by Wahi_B)
I have absolutely no idea how to do that.
Have you learnt this topic in school yet? What qualification are you doing and where did you get the question from?
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Wahi_B
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(Original post by Sir Cumference)
Have you learnt this topic in school yet? What qualification are you doing and where did you get the question from?
I have but I've never had these question before. I'm only in Year 9, I just started.
The question is part of a homework.
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Notnek
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(Original post by Wahi_B)
I have but I've never had these question before. I'm only in Year 9, I just started.
The question is part of a homework.
You’re in year 9 but this is A Level further maths level. Are you aware of that? Is your school giving you A Level work?
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Notnek
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(Original post by Wahi_B)
I have but I've never had these question before. I'm only in Year 9, I just started.
The question is part of a homework.
Actually was this given to you in physics lessons or maths lessons?
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Wahi_B
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(Original post by Sir Cumference)
You’re in year 9 but this is A Level further maths level. Are you aware of that? Is your school giving you A Level work?
OH. I had no idea but they do make it very difficult.
This is actually a Physics homework but because it required maths I clicked this category. Probably shouldn't have.
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Wahi_B
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(Original post by Sir Cumference)
Actually was this given to you in physics lessons or maths lessons?
Yeah. Physics. Sorry may have confused you.
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Notnek
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(Original post by Wahi_B)
Yeah. Physics. Sorry may have confused you.
Ok it looks like you’re learning GCSE physics which makes more sense. Do you know how to find kinetic energy?
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Wahi_B
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(Original post by Sir Cumference)
Ok it looks like you’re learning GCSE physics which makes more sense. Do you know how to find kinetic energy?
Yes.
It is 1/2 x Mass x Velocity squared
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Notnek
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(Original post by Wahi_B)
Yes.
It is 1/2 x Mass x Velocity squared
Ok so you need to find the initial kinetic energy and then the final kinetic energy and then subtract them to find the change in kinetic energy. The change in kinetic energy is equal to the work done by the braking force. Try this and if you get stuck please say specifically what you don’t get.
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Notnek
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(Original post by Wahi_B)
Yes.
It is 1/2 x Mass x Velocity squared
Wait you mentioned above that you’ve done the question now. Is that right?
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Wahi_B
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Sorry I don't think I specified before but there was a part before this and it was to calculate the kinetic energy that was lost due to the braking and I got
47,250J. I just don't get what you mean by how the change in kinetic energy is EQUAL to the work done BY the breaking force.
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Wahi_B
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#20
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(Original post by Sir Cumference)
Wait you mentioned above that you’ve done the question now. Is that right?
I did find out the answer but I don't know HOW I am supposed to get it.
The answer I got was 300kg x 3 m/s x 1/2
But why is the half there?
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