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> Police Car, Help required badly
deckearns
Posted: Mar 13 2012, 01:18 AM


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Robittybob1, Apologies, you are more correct than me. I rounded everything as whole seconds were good enough units for what I need. I should have stated this!

I used the quadratic formula once I was able to write things in terms of t:

using the quadratic formula:

a=1 b=-52 c= +198

t = -b +or- route b 4ac/2a (sorry I cannot show formula properly, note to web master - it would be better to have symbols and characters as an option instead of smilies! Just saying)..

Anyway:

a=1 b=-52 c= +198

so:

t = 52+- route -52 4.198/2

t = 52+- route 2704 792/2

t = 52+- route 1912/2

Answer1 = : 52 + 43.726422218150892295854760201079/2

= 47.86321110907544614792738010054 seconds

Answer2 = : 52 - 43.726422218150892295854760201079/2

= 4.1367888909245538520726198994605 seconds

I still notice that I still have a different answer to you but it's a tiny difference even after rounding (47.8632 v's 47.9085). I cannot know where the difference comes about, maybe some rounding loss between our working calculations (I rounded nothing in the above, I used the regular windows calculator. If I opened up to even more decimals I'm sure the decimal part of the answer would be even different again (more accurate).

There will always be two answers when solving a quadratic, the answer of 4 seconds cannot be correct so the other answer is chosen.

Thanks again
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Robittybob1
Posted: Mar 13 2012, 01:44 AM


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were you using the formula found at http://www.purplemath.com/modules/quadform.htm to solve quadratic equation?
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deckearns
Posted: Mar 13 2012, 07:37 AM


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Yes, that's the formula. Instead of using 'x' I replaced with 't', that's the only (tiny) difference I made to the formula. It's a pity we can't illustrate symbols here more, like square root etc. The way I had to display it wasn't very easy to read. Apologies. That link you posted is a good site. I've just read about the quadratic formula. Well written and explained, I'll be definitely visiting that site again..
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boit
Posted: Mar 13 2012, 04:02 PM


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My crude method of using closing speed (and repeated iteration for the second part) yielded a rounded off time of 34 seconds before adding the 14 seconds. So where was I failing with the quadriatic equation? t=-B-[(


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Boit was last taught physics in class way back in 1994. Whatever he's learnt thereafter is purely by personal effort through this forum and searching the net. He is not an authority in any matter science. Unless with clear referrence, what he puts forward is his own understanding of what he has read and may not always be correct. Peace.
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boit
Posted: Mar 13 2012, 09:19 PM


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http://www.purplemath.com/modules/quadform.htm
Thanks to Robbitybob1 I'm able to see that formula clearly (it helps now that am seeing it on the computer screen and not a phone as was the case earlier).


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Boit was last taught physics in class way back in 1994. Whatever he's learnt thereafter is purely by personal effort through this forum and searching the net. He is not an authority in any matter science. Unless with clear referrence, what he puts forward is his own understanding of what he has read and may not always be correct. Peace.
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