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# Physics maths question watch

1. Does anyone know how to solve this?

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2. (Original post by goodwinning)
Does anyone know how to solve this?

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4.1 t=3 so . Calculate that.

4.2 v=200 so . Solve that.
3. (Original post by BuryMathsTutor)
4.1 t=3 so . Calculate that.

4.2 v=200 so . Solve that.
Right, I'm alright for 4.1 now but I'm stuck on how to solve for t on the second one.

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4. (Original post by goodwinning)
Right, I'm alright for 4.1 now but I'm stuck on how to solve for t on the second one.
You need to rearrange the equation to make t the subject
5. Ok so I've got 200/230 = 1-e^-0.1t so far, now I have to take the ln right?

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6. (Original post by goodwinning)
Ok so I've got 200/230 = 1-e^-0.1t so far, now I have to take the ln right?

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Yes use natural logs on both sides
7. You shouldn't take natural logs until the equation has e ^ power as a subject
8. (Original post by Muttley79)
You shouldn't take natural logs until the equation has e ^ power as a subject
Yeah I figured as I was doing it. So I've now got e^-0.1t = -200/230 +1 and I suppose now I can take natural logs of both sides. Correct?

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9. How will you deal with the negative power?
10. (Original post by Muttley79)
How will you deal with the negative power?
Once I've take natural log of both sides, I'll then multiply both sides by negative 1.

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11. Once I've take natural log of both sides, I'll end up with -0.1t=ln-200/230 + 1 and il divide both sides by -0.1

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Updated: January 20, 2015
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