Maths & Physics Help

[astarmathsandphysics]

The second part of the question needs help.
Q.The air in a bicycle tyre has a volume of 1000cm3 and a pressure of 2.5 atmospheres. If the air is released ( at the same temperature) so its pressure is 1 atmosphere, what is the volume of the air?

This part needs help

A bicycle has a volume of 100cm3 and is now used to pump up the tyre. After 1 stroke of the pump, what is the presure in the tyre?

Thanks

pV=constant so 2.5x1000=2500=pV=1xV so V=2500cm^3
The air had volume of 2500 at 1atmosphere but we put in an extra 100 so new volume at 1 atmosphere is 2600cm^3
pV=1X2600=px1000 so p=2.6 atmospheres.

[hyebyekadal]

um..ur q is not quite clear so can you like say which paper? and year?

[nid404]

pV=constant so 2.5x1000=2500=pV=1xV so V=2500cm^3
The air had volume of 2500 at 1atmosphere but we put in an extra 100 so new volume at 1 atmosphere is 2600cm^3
pV=1X2600=px1000 so p=2.6 atmospheres.

I tried the same thing earlier but the answer to this question is 1.1 atmospheres. How do you derive that?
 And this question was found in a  physics textbook for IGCSE known as Physics For You by Keith Johnson. I don't know whether it was taken from any past paper.

 anyways thanks for your help.

[SGVaibhav]

do u have that book in a ebook?

[astarmathsandphysics]

pV=constant so 2.5x1000=2500=pV=1xV so V=2500cm^3
The air had volume of 2500 at 1atmosphere but we put in an extra 100 so new volume at 1 atmosphere is 2600cm^3
pV=1X2600=px1000 so p=2.6 atmospheres.

I tried the same thing earlier but the answer to this question is 1.1 atmospheres. How do you derive that?
 And this question was found in a  physics textbook for IGCSE known as Physics For You by Keith Johnson. I don't know whether it was taken from any past paper.

 anyways thanks for your help.

How can youn pump in 100cm^3 more air and have the pressure fall from 2.5 to 1 atmosphere?

[SGVaibhav]

What are all the possible ways to measure the distance from the screen to the centre of the lens?

If possible, can u show it with a diagram?

[astarmathsandphysics]

Try lining it up with a ruler or use a compass.

[SGVaibhav]

By the way... how do i write that in the paper?
there r many answers.
in markscheme they just write, correct method shown
i cannot ask my teacher also, because i have holidays.
so can u show me few ways

[astarmathsandphysics]

Open your compass so ene end touches the edege of the lens and the other touches the edge of the compass. Then you can use that same distance anywhere.

[SGVaibhav]

hmmm.
he thing is that it is Alternative to Practical Paper, not a practical paper.
so we have to write methods to measure. if the thing would be in front of me, i would have measured in some crappy way.  but over here, we cant do that

[astarmathsandphysics]

Ok then that would be your method. Having measured the distance with a compass, you can find the distance by lining the compass up with a ruler.

[SGVaibhav]

hmm
i think i am not able to express my question clearly.
i will show u the link to the exact question, that will help

http://www.freeexampapers.com/FreeExamPapers.com_.php?__lo=SUdDU0UvUGh5c2ljcy9DSUUvMjAwMiBOb3YvMDYyNV93MDJfcXBfNi5wZGY=
Q5)b) (can u show me atleast 2 methods please)

Thanx

[nid404]

pV=constant so 2.5x1000=2500=pV=1xV so V=2500cm^3
The air had volume of 2500 at 1atmosphere but we put in an extra 100 so new volume at 1 atmosphere is 2600cm^3
pV=1X2600=px1000 so p=2.6 atmospheres.

I tried the same thing earlier but the answer to this question is 1.1 atmospheres. How do you derive that?
 And this question was found in a  physics textbook for IGCSE known as Physics For You by Keith Johnson. I don't know whether it was taken from any past paper.

 anyways thanks for your help.

How can youn pump in 100cm^3 more air and have the pressure fall from 2.5 to 1 atmosphere?

I'll answer the question I posted. I know that's absurd but it's just to make sure others reading it do not get it wrong.

Q. a)The air in a bicycle tyre has a volume of 1000cm³ and a pressure of 2.5 atmospheres. If the air is released ( at the same temperature) so its pressure is 1 atmosphere, what is the volume of the air?

b)A bicycle has a volume of 100cm³ and is now used to pump up the tyre. After 1 stroke of the pump, what is the presure in the tyre?

Ans:

      (a)  V1= 1000 cm³, P1= 2.5 atm. V2= ?, P2= 1 atm.

      Using Boyle’s  Law,

            P1V1 = P2V2

      V2 = P1V1/P2

                  = 2500 cm³

      (b) According to Boyle’s law,

      Pressure and volume is inversely proportional to each other,

      Hence if volume decreases, the pressure increases but in same ratio,

      Since the volume of the pump is 100 cm³, and volume of the tyre is 1000cm³, the ratio of the decrease in volume after one stroke = 100/1000=0.1

      Hence the ratio by which the pressure will increase is 0.1 atm.

      Hence total pressure in the tyre = 1 atm + 0.1 atm

                                    = 1.1 atm

[astarmathsandphysics]

   Hence the ratio by which the pressure will increase is 0.1 atm.

      Hence total pressure in the tyre = 1 atm + 0.1 atm

                                    = 1.1 atm


THE AIR IN THE TYRE IS NEVER AT A PRESSURE OF 1 ATM. IT IS 2.5 ATM

Sorry to write in capitals but I had to make you read this.

[astarmathsandphysics]

It is only a 1 mark question. Why do you have nightmares? Use a meter rule either on the bench or in a clamp.