You are Here: Home >< Maths

# Trouble with variable acceleration

Announcements Posted on
Would YOU be put off a uni with a high crime rate? First 50 to have their say get a £5 Amazon voucher! 27-10-2016
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},

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: June 16, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

Find out here

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams