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# Trouble with variable acceleration Watch

1. I have a question which I dont understand where in going wrong:
A particle is 2kg and moves along AB under the constant action of force which at time t has magnitude 0.3sqrt(t). It acts in direction AB. When t=0, the particle passes through A at 5m/s. At t=8 it reaches B. Calculate AB distance.

So what I got is a=F/m = 0.3root(t)/2
So V=0.1t^(3/2) + c
At t=0, v=5 so c=5
So s = 0.04t^(5/2) +5t +c
At time t, displacement is 0 so c=0
So the final equation is s=0.04t^(5/2) +5t but when I put 8 in, I get 47.2. The answers say 54.72. What am I getting wrong?
2. (Original post by Bobrey)
I have a question which I dont understand where in going wrong:
A particle is 2kg and moves along AB under the constant action of force which at time t has magnitude 0.3sqrt(t). It acts in direction AB. When t=0, the particle passes through A at 5m/s. At t=8 it reaches B. Calculate AB distance.

So what I got is a=F/m = 0.3root(t)/2
So V=0.1t^(3/2) + c
At t=0, v=5 so c=5
So s = 0.04t^(5/2) +5t +c
At time t, displacement is 0 so c=0
So the final equation is s=0.04t^(5/2) +5t but when I put 8 in, I get 47.2. The answers say 54.72. What am I getting wrong?
Can't see anything wrong with your working.

I suspect a typo in their answer.
3. (Original post by ghostwalker)
Can't see anything wrong with your working.

I suspect a typo in their answer.
Oh - Thanks!
4. I think you'll find it's 0.08t^(5/2), not 0.04.

(funny how it says 'constant action of force' when it's a non-constant force btw. Seems just a tad potentially misleading)
5. (Original post by physicist 2016)
I think you'll find it's 0.08t^(5/2), not 0.04.
That would give an acceleration of 0.3\sqrt{t} and require a force of 0.6\sqrt{t},

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