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# physics question..HELP! watch

1. hi
really cant seem to work this question out:

at the start of a journey the temp and pressure inside a car tyre were 17 degrees and 300kPa.during the journey the pressure was 350kPa
calculate the temp during the journey

thanx
2. hey pls cmon ppl!!!
3. Is the volume of the gas Constant?
4. is doesnt actually say..but i reckon it should be coz its inside a car tyre..
5. Remember the relationship between pressure and temperature, p = kT, therefore p/T = k, so p1/T1 = p2/T2

To work out T2 therefore you have p2T1/p1, so in this case:

(350 * 17) / 300 = 20 degrees (to 2 significant figures)

(it is ok to leave the pressures as kPa etc because both of them use the same units).
6. P1V1/T1 = P2V2/T2, but V1=V2, so P1/T1 = P2/T2, so T2 = P2T1/P1

Where P2 = 350,000
P1 = 300,000
T1 = 17+273 (It should be in Kelvin)
7. Don't forget though that the temperature must be converted into Kelvins first i think.
8. (Original post by Rebuke)
Remember the relationship between pressure and temperature, p = kT, therefore p/T = k, so p1/T1 = p2/T2

To work out T2 therefore you have p2T1/p1, so in this case:

(350 * 17) / 300 = 20 degrees (to 2 significant figures)

(it is ok to leave the pressures as kPa etc because both of them use the same units).

thanx sooooo much 4 ure help im still kinda confused as to how u rearraged the formula to find T2=p2*T1/p1
sorry im jus kinda slow....
xxxx
9. Oops, you're right, temperature does have to be converted into Kelvin first so the answer I gave is wrong

As for re-arranging it, you take p = kT, divide by T to get p/T = k

Now, assuming the volume doesnt change, that k will be the same in both circumstances, so if you have the two sets of values you can show that p1/T1 = k and p2/T2 =k, i.e. p1/T1 = p2/T2

Then multiply by T2 to get p1T2/T1 = p2, divide by p1 to get T2/T1 = p2/p1, then multiply by T1 to get T2 = p2T1/p1

Now, the bit I forgot as pointed out by Willa and female_engineer is that you have to convert the temps into Kelvin first by adding 273 to them, so 17 degrees C = 290 degrees kelvin

Now you get (350 * 290) / 300 = 338 degrees Kelvin, now subtract 273 to get degrees C and you get 65 degrees C (to 2 significatn figures).
10. hey thanx alot guyz
really appreciate ure help!!

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