can any one please help me with this phy p4 question

[nischal shrestha]

i dnt know wat is the logic behind filling this table

 

[Fauziya]

yes plzz..too hav the same prblm...

 

[webfactor]

CAn you please tell the year and question number so I can see it

 

[Virtuoso]

Work done on the gas= Pressure* change in volume
u can use this formula to get the work done on the gas ... remember it is work done on the gas
and
for internal energy u can use
u=q+w

 

[Fauziya]

i cud get for the work done on gas from P ---> Q its 240J.....But i dnt get it for R ----> P

 

[nischal shrestha]

i still don't get it. the mark scheme for this question (9702_w10_ms_41) is quite wierd. the table for heating in ms and heat supplied to gas in qp is confusing me??
_

 

[usamah2702]

This is what i did
hope this helps:

from P---Q the work done was already calculated in (ii) so its 240J
so according to the formula Increase in internal energy=work done + heat supplied
so for P----Q Increase in I.E (u) is 240 (the work done) - 600 (the heat supplied) = -360 (internal energy)
from Q----R the increase in internal energy is 0 (work done) + 720 (heat supplied)= 720
from R-----P the Internal energy stays the same at the end cuz the total energy will be zero so it remains as -360 (from P---Q) the work done can be calculated:
workdone=increase in I.E - heat supplied
so WD= -360 - 480 = -840
I checked wid some teachers they said it was correct.

the marking scheme has different answers but the values for heating supplied are also different.

 

[nischal shrestha]

thanks usamah2702, but m still nt satisfied wid it. just can't believe that the ms is wrong???!!

 

[Fauziya]

usamah2702 thnx....but the mark scheme has very different answers....its jst confusing.....!!

 

[zeebujha]

The mark scheme is just plain wrong! However, the mark scheme does demonstrate that the net work done is 0.

 

[Fauziya]

then how do we do this ques.???

 

[nischal shrestha]

what a mind blowing stupid question with an annoying mark scheme!