Stupid Basic Maths Question

Lucifer666

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I want to start off by saying that I probably already know the answer to this question from an exercise I didn't even think would exist in my course due to how ridiculously easy it is, but I am beyond sleepy right now and can't force it out of my brain. I'm pulling an all-nighter to finish up some work, and I can no longer think. I've gone mad. I'm aware this is a stupid question.

So I'm given the formula d=0.0065v^2 + 0.75v
a) (Some long useless info here) basically translates into find d when v is 50

What I did:
d=0.0065(50^2) + 0.75(50)
d=0.0065(2500) + 37.5
d=16.25 + 37.5
d=53.75 m (The unit is metres according to the question)

That's right, right? I.. no longer have the power to check for myself.

b) Find v when d is 100 metres
100=0.0065v^2 + 0.75v
I uh, don't seem to remember what to do when there are different powers of a variable being added. Look I know this sounds ridiculous, but I need all the help I can get right now. I'm about to collapse.

I'm gonna try to proceed:
100=v(0.0065v +0.75)
100/(0.0065v + 0.75) = v
Wait what? No, I can't find v in terms of v..

Thanks in advance gyus

edit: My bad. I'm aware this should've been in Ask GBAtemp but there would be no spaces between the lines and it all looks squished and uncomfortable to read, so yeah.
 

Tom Bombadildo

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Damn...FAST beat me to it >.< But yeah, A is INCORRECT I LIED SORRY and for b just subtract 100 and plug it into the quadratic equation.

To expand upon his suggestion, though, here's what the equation should look like:

-.75±SQRT.75^2-(4*.0065*-100)
-----------------------------------------
2*.0065
 

Lucifer666

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Hm, I don't ever remember seeing a formula like this. What math are you taking?

This is just my IGCSE maths course, fairly simple. I'm willing to bet this formula isn't real but just made of for the sake of this question. I guess I can type out the entire question for you.
The stopping distance d m of a car travelling at v km/h is given by d = 0.0065v2 + 0.75v
a) Find the stopping distance of a car travelling at 50 km/h
b) Estimate the speed of a car which takes 100 m to stop

Thanks a lot FAST6191 and Suprgamr232!
But.. hang on, something's not quite right. I know for a fact that the answers PDF provided with my book says the answer is 110 km/h as an estimate. (I don't trust it, it sometimes has a lot of mistakes)

Replacing v with 110 in the equation doesn't give me anything close to 100. Either it's another mistake, or I'm just really crapping out at the moment.
 

Tom Bombadildo

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Hm, I don't ever remember seeing a formula like this. What math are you taking?

This is just my IGCSE maths course, fairly simple. I'm willing to bet this formula isn't real but just made of for the sake of this question. I guess I can type out the entire question for you.
The stopping distance d m of a car travelling at v km/h is given by d = 0.0065v2 + 0.75v
a) Find the stopping distance of a car travelling at 50 km/h
b) Estimate the speed of a car which takes 100 m to stop

Thanks a lot FAST6191 and Suprgamr232!
But.. hang on, something's not quite right. I know for a fact that the answers PDF provided with my book says the answer is 110 km/h as an estimate. (I don't trust it, it sometimes has a lot of mistakes)

Replacing v with 110 in the equation doesn't give me anything close to 100. Either it's another mistake, or I'm just really crapping out at the moment.
B...when I plug in 110 I get 140. So...I think your book is wrong...it's more like...
78.46

WARNING: DON'T LOOK IN THE SPOILERS IF YOU DON'T WANT THE ANSWERS
 
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