Math Is Fun Forum

Aartt

Member

Registered: 2010-12-14

Posts: 136

Confuzzling equations

ok so im learning about the kinectimatic equations and i got stuck on ow exactly these steps work here is the steps

(0 m/s)2 = (26.2 m/s)2 + 2*(-9.8m/s2)*d

0 m2/s2 = 686.44 m2/s2 + (-19.6 m/s2)*d

(-19.6 m/s2)*d = 0 m2/s2 -686.44 m2/s2

(-19.6 m/s2)*d = -686.44 m2/s2

d = (-686.44 m2/s2)/ (-19.6 m/s2)

d = 35.0 m

and when do you know when your supposed to use sqrt or powered by 2?

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Im a 6th grader(ya your all thinking what is he doing here. My answer is I <3 Math and i cannot get enough) I also like Science like Chemistry and Physics(even though i know about nothing about them i still love them because the include the word "MATH" )

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Confuzzling equations

Hi Aartt;

Whose steps are those?

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Aartt

Member

Registered: 2010-12-14

Posts: 136

Re: Confuzzling equations

here is the website http://www.physicsclassroom.com/Class/1DKin/u1l6c.cfm

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Im a 6th grader(ya your all thinking what is he doing here. My answer is I <3 Math and i cannot get enough) I also like Science like Chemistry and Physics(even though i know about nothing about them i still love them because the include the word "MATH" )

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Confuzzling equations

Hi Aart;

What I mean it is formatted fine over there but (26.2 m/s)2 is not the same as (26.2 m/s)². One can mean 52.4 m/s while the other is 686.44 m²/s²

I know all the kids are using the shortcut notation but I think you want to do it the right way.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Aartt

Member

Registered: 2010-12-14

Posts: 136

Re: Confuzzling equations

ok but could you like explain from like all the way from the beginning cause i dont even see how 52.4 is equal to 686.44m²/s²

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Im a 6th grader(ya your all thinking what is he doing here. My answer is I <3 Math and i cannot get enough) I also like Science like Chemistry and Physics(even though i know about nothing about them i still love them because the include the word "MATH" )

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Confuzzling equations

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Confuzzling equations

hi Aartt

(0 m/s)2 = (26.2 m/s)2 + 2*(-9.8m/s2)*d

0 m2/s2 = 686.44 m2/s2 + (-19.6 m/s2)*d

(-19.6 m/s2)*d = 0 m2/s2 -686.44 m2/s2

(-19.6 m/s2)*d = -686.44 m2/s2

d = (-686.44 m2/s2)/ (-19.6 m/s2)

d = 35.0 m

This looks like the equation

with

so rearrange to give

Does that make sense?

My advice is the usual  "Break the problem down into short, easier steps."  In particular:

(i) Identify which you know out of v, u, a, d, t and which you want to find.
(ii) Write down the correct equation.
(iii) If all the units are correct, m/s etc, then leave them out during the calculation
(iv) Substitute the numbers.
(v) Work out the missing letter.
(vi)  Put in the correct units.
(vii)  Is this answer sensible for the problem?

Bob

Last edited by Bob (2010-12-23 21:33:32)

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Aartt

Member

Registered: 2010-12-14

Posts: 136

Re: Confuzzling equations

D: uhhh still confused why didnt you add the two

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Im a 6th grader(ya your all thinking what is he doing here. My answer is I <3 Math and i cannot get enough) I also like Science like Chemistry and Physics(even though i know about nothing about them i still love them because the include the word "MATH" )

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Confuzzling equations

hi Aartt

This is the equation.

These are the numbers:

so

so

so

Does that explain it?

Bob

Last edited by Bob (2010-12-24 06:37:15)

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

Aartt

Member

Registered: 2010-12-14

Posts: 136

Re: Confuzzling equations

hmmm ok so i kind of flip the equation  over

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Im a 6th grader(ya your all thinking what is he doing here. My answer is I <3 Math and i cannot get enough) I also like Science like Chemistry and Physics(even though i know about nothing about them i still love them because the include the word "MATH" )

sameer mishra

Member

Registered: 2010-08-27

Posts: 64

Re: Confuzzling equations

A bulit is fired with velocity (v=2t). It strikes the tree having resistence 5 newton. Find velocity  vs distance travell plot &total distance travell by bullet before stop as well as acceleration vs time plotl

Bob

Administrator

Registered: 2010-06-20

Posts: 10,623

Re: Confuzzling equations

hi sameer mishra

I'm a bit confused about your variables here.

You say v = 2t  ( velocity equals 2t whatever t is; or do you want t to stand for time?)

Resistence = 5N  (OK that makes sense to me but without knowing the mass of the bullet, how can I work out the deceleration?)

And are you asking for graphs, or values or both.

The usual graphs for this sort of problem would be velocity up and time across and acceleration up and time across.

See below for sketches of what these would be like.  The deceleration is constant so the bottom graph is a horizontal line; the velocity steadily decreases so a straight line with negative gradient.   I've not put in any values as I'm not sure from your post what they are.  The grid lines have no special significance as I haven't got a scale yet.

The total distance travelled is the yellow area on the V / t graph.  (= area under the velocity graph)

later edit:

It occurs to me that if you are given the velocity before it hits the tree and the time taken to come to rest then all is solved.

Put that value of v and t on the V / t graph.  The area is the distance travelled and the gradient gives the acceleration (negative).

Is this enough? or post more details please.

Bob

Last edited by Bob (2011-01-22 02:48:31)

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob