- #1

GregA

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Not sure if this is the correct place to post (not homework because I am studying maths and mechanics in my own time...not a general maths problem either) but...

I have been working on a problem for a while now that has not only kept me up into the early hours of the morning, but has also woken me up at an early hour, and is just getting frustrating now The problem is as follows:

"A body moving in a straight line with a constant acceleration takes 3 seconds and 5 seconds to cover two succsessive distances of 1m. Find the acceleration (Hint: use distances of 1m and 2m from the start of the motion)"

What I know is the distance covered at two different points of time...I do not know the starting or ending velocity. I have tried numerous approaches (of which most result in garbage) but the one I'm rolling with so far is as follows:

Though I don't know the velocity(v), I can express it in terms of u

s=1/2(v+u)t can be transposed to v=(2s/t)-u

when t =3...v = (2/3)-u

when t =8...v2 = (4/8)-u

a = (v-u)/t...or a = (v2-v)/t

a = ((4/8-u) - (2/3-u))/8-3

a =(-4/24)/5...=-1/30m/s^2

problem is that the answer in the book is given as -1/15m/s^2...this answer is twice mine...Where am I going wrong? Is there a blatantly obvious flaw in my understanding that makes my working look ridiculous or just a little something I am missing...please help

I have been working on a problem for a while now that has not only kept me up into the early hours of the morning, but has also woken me up at an early hour, and is just getting frustrating now The problem is as follows:

"A body moving in a straight line with a constant acceleration takes 3 seconds and 5 seconds to cover two succsessive distances of 1m. Find the acceleration (Hint: use distances of 1m and 2m from the start of the motion)"

What I know is the distance covered at two different points of time...I do not know the starting or ending velocity. I have tried numerous approaches (of which most result in garbage) but the one I'm rolling with so far is as follows:

Though I don't know the velocity(v), I can express it in terms of u

s=1/2(v+u)t can be transposed to v=(2s/t)-u

when t =3...v = (2/3)-u

when t =8...v2 = (4/8)-u

a = (v-u)/t...or a = (v2-v)/t

a = ((4/8-u) - (2/3-u))/8-3

a =(-4/24)/5...=-1/30m/s^2

problem is that the answer in the book is given as -1/15m/s^2...this answer is twice mine...Where am I going wrong? Is there a blatantly obvious flaw in my understanding that makes my working look ridiculous or just a little something I am missing...please help

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