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A particle is moving with uniform acceleration. If it starts from rest and 5 seconds later has a speed of 18 ms-1. Find the distance it has travelled.

My method:

u = 0 [initial velocity]

t = 5s [time]

a= 18ms-1 [acceleration]

so I used the following formulae to find the distance it had travelled:

s=vt+1/2at^2

as we do not know the initial velocity, I marked that as "0" and just equating the coefficent aboves into their letters for that formulae.

s = 0 + 1/2(18)(5)^2 = 187.5 m

which is wrong it should be 45m

Any idea, where I am going wrong...I have a feeling I used the speed variable incorrectly.

My method:

u = 0 [initial velocity]

t = 5s [time]

a= 18ms-1 [acceleration]

so I used the following formulae to find the distance it had travelled:

s=vt+1/2at^2

as we do not know the initial velocity, I marked that as "0" and just equating the coefficent aboves into their letters for that formulae.

s = 0 + 1/2(18)(5)^2 = 187.5 m

which is wrong it should be 45m

Any idea, where I am going wrong...I have a feeling I used the speed variable incorrectly.

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#2

(Original post by

A particle is moving with uniform acceleration. If it starts from rest and 5 seconds later has a speed of 18 ms-1. Find the distance it has travelled.

**DOJO**)A particle is moving with uniform acceleration. If it starts from rest and 5 seconds later has a speed of 18 ms-1. Find the distance it has travelled.

s=(u+v)/2 . t

s = 9x5

s = 45m.

You do know the initial speed (rest) and don't know the acceleration.

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(Original post by

u=0, v=18, t=5, s=?

s=(u+v)/2 . t

s = 9x5

s = 45m.

You do know the initial speed (rest) and don't know the acceleration.

**Gaz031**)u=0, v=18, t=5, s=?

s=(u+v)/2 . t

s = 9x5

s = 45m.

You do know the initial speed (rest) and don't know the acceleration.

so I am slightly unsure on how you came to that conclusion because if you equate the co-efficents U,V, and T to find S, everything cancels out because the initial velocity is 0 and the acceleration is 0.

Thanks.

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#4

(Original post by

Thanks for you answer, I can see how you have got that answer, but what is confusing me is that the formulae for s = ut + 1/2at^2 .

so I am slightly unsure on how you came to that conclusion because if you equate the co-efficents U,V, and T to find S, everything cancels out because the initial velocity is 0 and the acceleration is 0.

Thanks.

**DOJO**)Thanks for you answer, I can see how you have got that answer, but what is confusing me is that the formulae for s = ut + 1/2at^2 .

so I am slightly unsure on how you came to that conclusion because if you equate the co-efficents U,V, and T to find S, everything cancels out because the initial velocity is 0 and the acceleration is 0.

Thanks.

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(Original post by

The acceleration isn't 0.

**Gaz031**)The acceleration isn't 0.

therefore s= ut + 1/2at^2

which is s=0(5) + 1/2 9(25) = 225/2 = 112.5 m , which is incorrect

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#8

(Original post by

Yeah true, acceleration is 9 right? a=v-u/t which is a = 18/2 = 9

therefore s= ut + 1/2at^2

which is s=0(5) + 1/2 9(25) = 225/2 = 112.5 m , which is incorrect

**DOJO**)Yeah true, acceleration is 9 right? a=v-u/t which is a = 18/2 = 9

therefore s= ut + 1/2at^2

which is s=0(5) + 1/2 9(25) = 225/2 = 112.5 m , which is incorrect

Just use the other appropriate formula.

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(Original post by

a=v-u/t

= (18-0)/5

=3.6 ?

**GoPat**)a=v-u/t

= (18-0)/5

=3.6 ?

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#10

You don't knoiw the acceleration from the question. You know that u=0, t=5 and v=18. You want to find s. So you should really use a formula with those 4 in, which is s= ((u+v)t)/2

If you want to find the acceleration, then use v=u+at, which means it comes out at 3.6

I think you need to look at the formulae again, as that's where you seem to be going wrong

If you want to find the acceleration, then use v=u+at, which means it comes out at 3.6

I think you need to look at the formulae again, as that's where you seem to be going wrong

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#11

(Original post by

A particle is moving with uniform acceleration. If it starts from rest and 5 seconds later has a speed of 18 ms-1. Find the distance it has travelled.

My method:

u = 0 [initial velocity]

t = 5s [time]

a= 18ms-1 [acceleration]

so I used the following formulae to find the distance it had travelled:

s=vt+1/2at^2

as we do not know the initial velocity, I marked that as "0" and just equating the coefficent aboves into their letters for that formulae.

s = 0 + 1/2(18)(5)^2 = 187.5 m

which is wrong it should be 45m

Any idea, where I am going wrong...I have a feeling I used the speed variable incorrectly.

**DOJO**)A particle is moving with uniform acceleration. If it starts from rest and 5 seconds later has a speed of 18 ms-1. Find the distance it has travelled.

My method:

u = 0 [initial velocity]

t = 5s [time]

a= 18ms-1 [acceleration]

so I used the following formulae to find the distance it had travelled:

s=vt+1/2at^2

as we do not know the initial velocity, I marked that as "0" and just equating the coefficent aboves into their letters for that formulae.

s = 0 + 1/2(18)(5)^2 = 187.5 m

which is wrong it should be 45m

Any idea, where I am going wrong...I have a feeling I used the speed variable incorrectly.

v=18 m/s

u=0 (at rest)

x=?

t=5 seconds

x= 1/2(u+v)t

= 1/2 * (18+0) * 5

=45

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(Original post by

You don't knoiw the acceleration from the question. You know that u=0, t=5 and v=18. You want to find s. So you should really use a formula with those 4 in, which is s= ((u+v)t)/2

If you want to find the acceleration, then use v=u+at, which means it comes out at 3.6

I think you need to look at the formulae again, as that's where you seem to be going wrong

**juno_the**)You don't knoiw the acceleration from the question. You know that u=0, t=5 and v=18. You want to find s. So you should really use a formula with those 4 in, which is s= ((u+v)t)/2

If you want to find the acceleration, then use v=u+at, which means it comes out at 3.6

I think you need to look at the formulae again, as that's where you seem to be going wrong

I have got the right answer so i think:

s=(0)(5)+1/2 3.6(25)= 45m

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#13

(Original post by

The speed bit in the question confused me at first, which gaz thankfully corrected.

I have got the right answer so i think:

s=(0)(5)+1/2 3.6(25)= 45m

**DOJO**)The speed bit in the question confused me at first, which gaz thankfully corrected.

I have got the right answer so i think:

s=(0)(5)+1/2 3.6(25)= 45m

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(Original post by

Yeah, that's right. But as the question didn't ask you to find the acceleration, you could've used the other equation I said. It's just a bit quicker for if you're short of time in exams, but if you've got enough time to do it that way then that's fine

**juno_the**)Yeah, that's right. But as the question didn't ask you to find the acceleration, you could've used the other equation I said. It's just a bit quicker for if you're short of time in exams, but if you've got enough time to do it that way then that's fine

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#15

can i say, im fairly certain you'll get given the equations in the formula book especially if OCR or Edexcel Math. you can also dervive all the equations using one of two ways. if u know one u can gett the rest mathematically as here:

http://www.plus2physics.com/linear_m...apter=1&page=3

but i dont understand it, or you can do the area under a graph using speed/time, distance time, findint the tangents etc i think thats here too or else pm me for mor hepl

good liuck!

http://www.plus2physics.com/linear_m...apter=1&page=3

but i dont understand it, or you can do the area under a graph using speed/time, distance time, findint the tangents etc i think thats here too or else pm me for mor hepl

good liuck!

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#17

(Original post by

The thing is that the M1 book only teaches you that equation in the form I used...So i was not aware of that other formulae until now. Maybe that other formulae was in the book , but i probably skimmed over it. Thanks all

**DOJO**)The thing is that the M1 book only teaches you that equation in the form I used...So i was not aware of that other formulae until now. Maybe that other formulae was in the book , but i probably skimmed over it. Thanks all

v=u+at (no s)

v^2=u^2+2as (no t)

s=ut+1/2at^2 (no v)

s= ((u+v)t)/2 (no a)

s=vt-1/2at^2 (no u)

So you just pick the formula that contains the 3 things you know, and the 1 you want to find out.

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(Original post by

can i say, im fairly certain you'll get given the equations in the formula book especially if OCR or Edexcel Math. you can also dervive all the equations using one of two ways. if u know one u can gett the rest mathematically as here:

**magiccarpet**)can i say, im fairly certain you'll get given the equations in the formula book especially if OCR or Edexcel Math. you can also dervive all the equations using one of two ways. if u know one u can gett the rest mathematically as here:

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