Rearranging equations.

[iAmiAdam]

Ok, this might be a long shot, but I need help rearranging the equations of motion, mainly because I'm shocking at maths and never really learnt how to do it.

So, I'm trying to make v the subject in the equation s=(u+v/2)t

If anyone can like teach me how to rearrange any equation, it'd be greatly appreciated.

 

[twentysix by twentyfive]

it's a question of multiplying, dividing, adding and subtracting the same things from both side of the equation.

so s=(u+v/2)*t

Divide both sides by t

s/t=(u+v/2)

Subtract u from both sides

s/t-u = v/2

Multiply both sides by 2

2(s/t-u)=v

QED

BTW - is your equation correct in the first place ??????????

 

[iAmiAdam]

Yeah, it just looks different, can't really replicated it exactly on here, But thanks, that's a great help, will probs be asking more questions though.

 

[twentysix by twentyfive]

Yeah, it just looks different, can't really replicated it exactly on here, But thanks, that's a great help, will probs be asking more questions though.

No worries - Simples

Lots of practice is the best advice. Just keep doing lots of examples. It becomes second nature after a bit and eventually you'll be able do the easier ones in your head

 

[iAmiAdam]

Yeah, i've kinda got that you change the sign e.g + to - and that you change times to divide, but I'm still a bit shaky when I have to times both sides by two or whatever.

 

[twentysix by twentyfive]

Yeah, i've kinda got that you change the sign e.g + to - and that you change times to divide, but I'm still a bit shaky when I have to times both sides by two or whatever.

Just use brackets as you need to. If you like use brackets all the time. They can be removed if redundant at the end. In computer coding I use far more brackets than I might need to just to be absolutely certain (the computer code then ignores what it can - but might be maginally slower I suppose).

And as for the sign changes - that's equivalent to adding, subtracting or multiplying, dividing the same factors on both sides. That's what you are formally doing - to keep the equation equal on both sides. If you think of it that way you can't go wrong really (well Hmmmph.....?)

 

[iAmiAdam]

Yeah, Just done the first three questions of this sheet, and It's going fairly well. Can I ask what kind of Computer coding you do? I'm also doing computing in college, which is Pascal Programming.

 

[twentysix by twentyfive]

Well a very long time ago I used Fortran, I've done some Basic too and some Hewlett Packard languages too but more recently I've used a mathematics software package called Mathematica (which can rearrange your equation for you - but don't do it as you need the practice) http://www.wolfram.com/ and had a go at Mathcad www.ptc.com/products/mathcad/ which is similar but not so powerful.

 

[marinyork]

You'll soon get used to the suvat equations. If you need any more help just post. The most important one is v = u + at.

 

[iAmiAdam]

Well a very long time ago I used Fortran, I've done some Basic too and some Hewlett Packard languages too but more recently I've used a mathematics software package called Mathematica (which can rearrange your equation for you - but don't do it as you need the practice) http://www.wolfram.com/ and had a go at Mathcad www.ptc.com/products/mathcad/ which is similar but not so powerful.

Ah I see, I might use that in future, cheers.

You'll soon get used to the suvat equations. If you need any more help just post. The most important one is v = u + at.

Thanks for the offer.

 

[marinyork]

Ah I see, I might use that in future, cheers.

You don't need to use Mathematica or Maple unless you're an undergraduate or you're genuinely interested. Most teachers haven't got a clue what these are, they are mostly used by mathematicians or people insightful enough to realise how useful they are.

 

[iAmiAdam]

So, If I have an initial velocity of 30ms-1 and a final velocity of 0ms-1, and the car is deccelerating at 10ms-2, I'll work out the displacement by doing;
(I'll use brackets for powers)

30(2) / 2*10 that equals 45?

 

[marinyork]

That's correct but I'd set it out under some sort of system and don't forget units. Like below.
For suvat it's best writing it out in some sort of system
s= u=30ms[sup]-1[/sup] v =0ms[sup]-1[/sup] a=10ms[sup]-2[/sup] t=

We have 3 pieces of information. We need v[sup]2[/sup]= u[sup]2[/sup] +2as and to rearrange either now or later.

(v[sup]2[/sup]- u[sup]2[/sup] )/(2a) =s
(0[sup]2[/sup]-30[sup]2[/sup])/(20) = 900/20 = 45 something what units do we need
(ms[sup]-1[/sup] )[sup]2[/sup] / ms[sup]-2

[/sup]m[sup]2[/sup]s[sup]-2[/sup] / ms[sup]-2[/sup]

one m cancels and the s[sup]-2[/sup] cancels so we're left with m metres does this sound reasonable? Yes, distance is measured in metres. So 45m

 

[iAmiAdam]

Sorted, cheers.

Now I'm struggling to work out how to find a runners average speed after she accelerates to a steady speed in 1.5s and runs the 100m in 10.49s.

So far, I've worked out that her average speed is 9.53[sup]ms-1 [/sup]but this doesn't really help me, I know I've probably got to split the run into two halves, an acceleration, and a steady speed, but that's figuring the tricky bit.

 

[marinyork]

lol it's moments like these you wish the forum had laTeX support.