M1: motion with uniform acceleration Watch

chevina
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Can anyone help me with this?

A car starts from rest at the bottom of a slope. It accelerates up the slope for 8 seconds at 1.5 m s^{-2}, then disengages the engine and coasts. If its acceleration is now -1 m s^{-2}, find the time between the car leaving the bottom of the slope and returning to it.

Thanks
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pyrolol
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The motion splits into two clear halves, so consider each separately?

Firstly - while it's accelerating. What do you know...."at rest" so u = 0, t = 8, and so on.
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Using the vusat/suvat (or some other mnemonic I've never heard) equations, try to find how far it goes up the slope.


Now look at the second part of the motion...it's falling back to where it started.
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So we know s = <what you found in the first part>, and we can find t.


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Remember to add the 8 seconds for the first bit on!
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chevina
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EDIT: answered my own question :p:

Another one though: why does s in the first part equal s in the second part?
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MathsStudent
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out of curiousity how come ur doing m1 after the exams are ova
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Pork and Beans
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(Original post by chevina)
EDIT: answered my own question :p:

Another one though: why does s in the first part equal s in the second part?
For the first part, you've travelled s metres from the starting point, so for the second part you need to travel s metres in the opposite direction to return to the starting point.
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bubblewit
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(Original post by MathsStudent)
out of curiousity how come ur doing m1 after the exams are ova
Not sure if this applies to the OP, but at my college we start the next year (Yr 13) after the exams up until the summer holidays for an extra few weeks of A2 study.
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chevina
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(Original post by Pork and Beans)
For the first part, you've travelled s metres from the starting point, so for the second part you need to travel s metres in the opposite direction to return to the starting point.
Oh ok. I must have misunderstood the question - in real life, if you turn the engine off, you still continue forwards for a while before going back down the slope.. The 'coasts' part confused me. Thanks
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