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Variable acceleration M2

see.png

I dont understand why they use t=1/3 and t=2?
And why did they multiply by 2 at the end?

thanks!
Original post by Zenarthra
see.png

I dont understand why they use t=1/3 and t=2?
And why did they multiply by 2 at the end?

thanks!


The question is asking for the distance travelled, not the displacement.

So starting from t=0, it moves forwards until t=1/3, and then backwards.

Hopefully, it's now clear.
Reply 2
Avatar for Zenarthra
Zenarthra
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Original post by ghostwalker
The question is asking for the distance travelled, not the displacement.

So starting from t=0, it moves forwards until t=1/3, and then backwards.

Hopefully, it's now clear.


Oh i understand, but why not just t=1 and t=2? O_O
Original post by Zenarthra
Oh i understand, but why not just t=1 and t=2? O_O


Why t=1?
Reply 4
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davros
16
Original post by Zenarthra
Oh i understand, but why not just t=1 and t=2? O_O


How does t = 1 help you?

The first two seconds are from t = 0 to t = 2.

The particle moves forwards from t = 0 to t = 1/3; then it stops and changes direction from t = 1/3 to t = 2 (it's still going until t = 3 but that's irrelevant because we're only measuring time until t = 2).
Reply 5
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Zenarthra
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Original post by ghostwalker
Why t=1?


Original post by davros
How does t = 1 help you?

The first two seconds are from t = 0 to t = 2.

The particle moves forwards from t = 0 to t = 1/3; then it stops and changes direction from t = 1/3 to t = 2 (it's still going until t = 3 but that's irrelevant because we're only measuring time until t = 2).


So i should just use the t values found, for these questions?
Reply 6
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davros
16
Original post by Zenarthra
So i should just use the t values found, for these questions?


I don't understand your question - you use the t values that are appropriate based on what the original question asks!

Why did you think that t = 1 would be a relevant value of t to use?
Original post by Zenarthra
So i should just use the t values found, for these questions?


You need the distance they travelled forwards plus the distance they travelled backwards after that. You must use the value of t for when they were stationary to find their position between the two parts of the motion.
Reply 8
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Zenarthra
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Original post by davros
I don't understand your question - you use the t values that are appropriate based on what the original question asks!

Why did you think that t = 1 would be a relevant value of t to use?

Oh they used t=1/2 because at t=1/3 v=0 :laugh:
If it was t=1/3 was positive and t=2 was positive would the distance travelled during 2 seconds be just the value for t=2?

Original post by ghostwalker
You need the distance they travelled forwards plus the distance they travelled backwards after that. You must use the value of t for when they were stationary to find their position between the two parts of the motion.


Ahh ok ty, i understand.
(edited 9 years ago)
Reply 9
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davros
16
Original post by Zenarthra
Oh they used t=1/2 because at t=1/3 v=0 :laugh:
If it was t=1/3 was positive and t=2 was positive would the distance travelled during 2 seconds be just the value for t=2?


As long as there's no change in direction, yes.

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