Need Help With Physics Paper 1 Questions

[dark_ruller1996]

Hey if anyone could solve and explain questions,
20 and 21, from oct/nov 2006, paper 1, 9702
That would be great.
For question 20, i don't get why the average kinetic energy is reduced
And for question 21 im using the formula p=qgh but i still don't get the correct answer.
I tried considering atmospheric pressure but i can't figure it out any help would be appericiated.

 

[h4rriet]

Hey if anyone could solve and explain questions,
20 and 21, from oct/nov 2006, paper 1, 9702
That would be great.
For question 20, i don't get why the average kinetic energy is reduced
And for question 21 im using the formula p=qgh but i still don't get the correct answer.
I tried considering atmospheric pressure but i can't figure it out any help would be appericiated.

20. The average K.E. gets reduced because the molecules with the highest K.E. leave. So the average becomes less.
21. You'll have to use pressure=rho x g x h.
Like this: 17.5 x (10^6) = (830 x 9.81 x h) + (1000 x 9.81 x 2000-h).

 

[dark_ruller1996]

20. The average K.E. gets reduced because the molecules with the highest K.E. leave. So the average becomes less.
21. You'll have to use pressure=rho x g x h.
Like this: 17.5 x (10^6) = (830 x 9.81 x h) + (1000 x 9.81 x 2000-h).

Thanks soo much