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# M2 Variable Acceleration - need help Watch

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!!

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Updated: August 19, 2016
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