You are Here: Home >< Maths

# M2 Variable Acceleration - need help

Announcements Posted on
TSR's new app is coming! Sign up here to try it first >> 17-10-2016
1. So the question is as follows; "A displacement, s metres, at time t seconds, of a particle from a fixed point is given by s=2t^2+3t-2.
i) Find the initial displacement and initial velocity.
ii) Find any times where the velocity is zero.
iii) Find any times where the particle is at the origin."
I have tried all 3 sections but for the first section i had a distance of -2 metres, for the second section I had a time of -0.75 seconds and for the third section I had 2 times of 0.5 seconds and -2 seconds. If anyone could help then that would be great as I'm not the strongest in Mechanics!
2. (Original post by abbiechantellex)
So the question is as follows; "A displacement, s metres, at time t seconds, of a particle from a fixed point is given by s=2t^2+3t-2.
i) Find the initial displacement and initial velocity.
ii) Find any times where the velocity is zero.
iii) Find any times where the particle is at the origin."
I have tried all 3 sections but for the first section i had a distance of -2 metres, for the second section I had a time of -0.75 seconds and for the third section I had 2 times of 0.5 seconds and -2 seconds. If anyone could help then that would be great as I'm not the strongest in Mechanics!
The answers you have calculated are all correct, well done!
3. (Original post by HapaxOromenon3)
The answers you have calculated are all correct, well done!
Wow, really?! They were negative and so I got very confused, is there any particular reason as to why they are negative?
4. (Original post by abbiechantellex)
Wow, really?! They were negative and so I got very confused, is there any particular reason as to why they are negative?
A negative displacement means it goes in the opposite direction to nornal. E.g. in coordinate geometry, (3,0) is 3 units to the right of the origin and (-3,0) is 3 units to the left of the origin.

Since t=0 is the time when we started measuring values of s, a negative time means that if we assume the equation for s was valid even before we started measuring, then the event happened however many seconds before we started measuring. That is, t=-0.75 means that the velocity was zero 0.75 seconds before we (the experimenter) started measuring s, assuming that the particle's motion followed the same equation for s in terms of t even though this was before we had started the experiment. Hopefully that makes sense!
5. (Original post by HapaxOromenon3)
A negative displacement means it goes in the opposite direction to nornal. E.g. in coordinate geometry, (3,0) is 3 units to the right of the origin and (-3,0) is 3 units to the left of the origin.

Since t=0 is the time when we started measuring values of s, a negative time means that if we assume the equation for s was valid even before we started measuring, then the event happened however many seconds before we started measuring. That is, t=-0.75 means that the velocity was zero 0.75 seconds before we (the experimenter) started measuring s, assuming that the particle's motion followed the same equation for s in terms of t even though this was before we had started the experiment. Hopefully that makes sense!
Yes that makes a lot more sense now, thank you so much!!

## 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: August 19, 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

### How does exam reform affect you?

From GCSE to A level, it's all changing

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