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# working out acceleration when given speed and distance watch

1. v= 17.5 ms-1
u= 0 ms-1
s = .20m

v^2=u^2+2as
v=u+2as
0=17.5+2*(a*.20)
-17.5=2*(a*.20)
8.75=a*.20
43.75=a

am i on the right lines
2. How did you lose your squares in:

v^2=u^2+2as

to

v=u+2as?

As a general note though, you're trying to find a, so rearrange the formula to be for a BEFORE putting any numbers in, it will make your life easier. You're putting the numbers in, then sorting it out.
3. (Original post by JoMo1)
How did you lose your squares in:

v^2=u^2+2as

to

v=u+2as?

As a general note though, you're trying to find a, so rearrange the formula to be for a BEFORE putting any numbers in, it will make your life easier. You're putting the numbers in, then sorting it out.
thanks for that, i realised after i posted it i should now have taken away the squares i did that cos i saw them on both side but realised it is v^2 and u^2 so would not be right to cancel them out
4. (Original post by Foster88)
thanks for that, i realised after i posted it i should now have taken away the squares i did that cos i saw them on both side but realised it is v^2 and u^2 so would not be right to cancel them out
That would be fine, but you'd need to sqrt the 2as
5. v^2=u^2+2as

v^2/u^2-2s=a

a= 0.4

hmm still seems wrong ? :/
6. v^2=u^2+2as
2as=v^2-u^2
a=(v^2-u^2)/2s
Then input the numbers. Try practicing more rearrangments, or deriving the other constant acceleration equations to get more comfortable with it.
7. (Original post by vandub)
v^2=u^2+2as
2as=v^2-u^2
a=(v^2-u^2)/2s
Then input the numbers. Try practicing more rearrangments, or deriving the other constant acceleration equations to get more comfortable with it.
wouldnt this give 0 as an answer though :/

i think i get it now sorry
8. (Original post by Foster88)
wouldnt this give 0 as an answer though :/
Nope.
a=(v^2-u^2)/2s
=17.5^2/(2*.2)
=306.25/.4
=765.625 ms^2
Why did you think it'd give 0?
9. (Original post by vandub)
Nope.
a=(v^2-u^2)/2s
=17.5^2/(2*.2)
=306.25/.4
=765.625 ms^2
Why did you think it'd give 0?
why i tried arranging the equations i was dividing the u^2 instead of minus(ing) it my bad
10. (Original post by Foster88)
why i tried arranging the equations i was dividing the u^2 instead of minus(ing) it my bad
Ah right. Although, you should know that dividing by 0 doesn't equal zero, instead it's undefined, as in, there is no answer, so it can't be done.
11. [QUOTE=Foster88;30862711]v= 17.5 ms-1
u= 0 ms-1
s = .20m

v^2=u^2+2as
v=u+2as
0=17.5+2*(a*.20)
-17.5=2*(a*.20)
8.75=a*.20
43.75=a

Are you sure s=0.2m?

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