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I'm confused with SUVAT equations when trying to work out t, i get different answers when using different equations to solve for t, could anyone help,

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#2

You may need to show us the question and your answer.

(Original post by

I'm confused with SUVAT equations when trying to work out t, i get different answers when using different equations to solve for t, could anyone help,

**beekydog**)I'm confused with SUVAT equations when trying to work out t, i get different answers when using different equations to solve for t, could anyone help,

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#3

**beekydog**)

I'm confused with SUVAT equations when trying to work out t, i get different answers when using different equations to solve for t, could anyone help,

The best thing to do is to list all the variables you are given, and the variable that the question is asking you for. e.g.

a=2, s=5, u=1, v=?

Then pick the formula that has all four of the variables in it and plug your numbers in.

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s=-1.5 u=22.4 v=0 a=-9.8 t=?

when I use s=(u+v/2)t and s=ut+0.5at2 i get different answers

when I use s=(u+v/2)t and s=ut+0.5at2 i get different answers

(Original post by

You may need to show us the question and your answer.

**mqb2766**)You may need to show us the question and your answer.

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#5

s= t*(u+v)/2

are your brackets correct? Distance is average velocity * time.

What was the original question?

are your brackets correct? Distance is average velocity * time.

What was the original question?

(Original post by

s=-1.5 u=22.4 v=0 a=-9.8 t=?

when I use s=(u+v/2)t and s=ut+0.5at2 i get different answers

**beekydog**)s=-1.5 u=22.4 v=0 a=-9.8 t=?

when I use s=(u+v/2)t and s=ut+0.5at2 i get different answers

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#6

**beekydog**)

s=-1.5 u=22.4 v=0 a=-9.8 t=?

when I use s=(u+v/2)t and s=ut+0.5at2 i get different answers

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ok, thank you! why isn't it valid?

(Original post by

s=(u+v/2)t this is not valid, you should re-derive the equations again. it is s = (u+v)t/2 ; classic mistake made at a level, which is to try to memorise every equation. Work on understanding the theory and then just derive the equations yourself, having a solid understanding of what is happening is far more useful

**mnot**)s=(u+v/2)t this is not valid, you should re-derive the equations again. it is s = (u+v)t/2 ; classic mistake made at a level, which is to try to memorise every equation. Work on understanding the theory and then just derive the equations yourself, having a solid understanding of what is happening is far more useful

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#8

Because its wrong. distance is average velocity*time.

That is not average velocity, which is (u+v)/2

That is not average velocity, which is (u+v)/2

(Original post by

ok, thank you! why isn't it valid?

**beekydog**)ok, thank you! why isn't it valid?

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#9

(Original post by

ok, thank you! why isn't it valid?

**beekydog**)ok, thank you! why isn't it valid?

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I haven't learnt the equation, I'm using it straight out of my textbook and that's how it appears in the book

(Original post by

its incorrect, the physics (and hence math) does not follow this rule, you cant just make up equations for convenience. As stated previously blindly trying to memorise every equation is not the best way to solve problems. I recommend learning the key classical physics principles in mechanics and derive the equations yourself. You will learn this much more effectively

**mnot**)its incorrect, the physics (and hence math) does not follow this rule, you cant just make up equations for convenience. As stated previously blindly trying to memorise every equation is not the best way to solve problems. I recommend learning the key classical physics principles in mechanics and derive the equations yourself. You will learn this much more effectively

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#11

(Original post by

I haven't learnt the equation, I'm using it straight out of my textbook and that's how it appears in the book

**beekydog**)I haven't learnt the equation, I'm using it straight out of my textbook and that's how it appears in the book

s = (u+v)t/2

And once again you've proved my point, if you have just copied random equations from a book without any understanding and have made a mistake copying & re-writing

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#12

https://www.youtube.com/watch?time_c...&v=rCi3exlvdo0

and many other places on the web. Just search for

deriving suvat

and it will be 1/2 hr well spent. Some may do it slightly differently, but its important to understand what the terms mean.

(Original post by

I haven't learnt the equation, I'm using it straight out of my textbook and that's how it appears in the book

and many other places on the web. Just search for

deriving suvat

and it will be 1/2 hr well spent. Some may do it slightly differently, but its important to understand what the terms mean.

**beekydog**)

I haven't learnt the equation, I'm using it straight out of my textbook and that's how it appears in the book

Last edited by mqb2766; 1 year ago

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#13

**mnot**)

s=(u+v/2)t this is not valid, you should re-derive the equations again. it is s = (u+v)t/2 ; classic mistake made at a level, which is to try to memorise every equation. Work on understanding the theory and then just derive the equations yourself, having a solid understanding of what is happening is far more useful

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I am sure that it says (u+v both over 2) multiplied by t, (sorry the way I typed it out earlier may have caused confusion aha)

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#15

(Original post by

I am sure that it says (u+v both over 2) multiplied by t, (sorry the way I typed it out earlier may have caused confusion aha)

**beekydog**)I am sure that it says (u+v both over 2) multiplied by t, (sorry the way I typed it out earlier may have caused confusion aha)

Do you still get a different answer? If so, can you post the numbers.

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#16

(Original post by

that is inappropriate advice for average students. if you are a genius with a deep understanding of physics then by all means derive the equations in the exam room. normal people should memorise 3 suvat formulae.

**the bear**)that is inappropriate advice for average students. if you are a genius with a deep understanding of physics then by all means derive the equations in the exam room. normal people should memorise 3 suvat formulae.

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Thanks I'll watch it now

T

(Original post by

https://www.youtube.com/watch?time_c...&v=rCi3exlvdo0

and many other places on the web. Just search for

deriving suvat

and it will be 1/2 hr well spent. Some may do it slightly differently, but its important to understand what the terms mean.

**mqb2766**)https://www.youtube.com/watch?time_c...&v=rCi3exlvdo0

and many other places on the web. Just search for

deriving suvat

and it will be 1/2 hr well spent. Some may do it slightly differently, but its important to understand what the terms mean.

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Yeah I definitely don't have a good understanding of physics haha

(Original post by

that is inappropriate advice for average students. if you are a genius with a deep understanding of physics then by all means derive the equations in the exam room. normal people should memorise 3 suvat formulae.

**the bear**)

that is inappropriate advice for average students. if you are a genius with a deep understanding of physics then by all means derive the equations in the exam room. normal people should memorise 3 suvat formulae.

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#19

**mnot**)

s=(u+v/2)t this is not valid, you should re-derive the equations again. it is s = (u+v)t/2 ; classic mistake made at a level, which is to try to memorise every equation. Work on understanding the theory and then just derive the equations yourself, having a solid understanding of what is happening is far more useful

they are the same thing?

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