physics paper 3, harder than hard

[Chucky]

what is the answer for the first question in radioactivity?

the one on how the reading doesn't decrease but increases?
they will mark on two specific points - BACKGROUND radiation and spontaneousness on radioactivity.
a similar question came in a previous year, so I knew this was the way to answer it:

the radiaoactive substance had decayed to a stable particle, but the counts reading did not decrease and there was still background radiation (youcan mention some sources of it too). the reading increased a bit too as radioactivity is random or spontaneous, so the background radiation can spike at times.

note : by an increase they dont mean a huge increase, just minor ups and downs as you could see in the graph. hence the best fit line was drawn.

 

[Zeus]

What did you guys get for the efficiency of the turbines ?

 

[kboss]

the one on how the reading doesn't decrease but increases?
they will mark on two specific points - BACKGROUND radiation and spontaneousness on radioactivity.
a similar question came in a previous year, so I knew this was the way to answer it:

the radiaoactive substance had decayed to a stable particle, but the counts reading did not decrease and there was still background radiation (youcan mention some sources of it too). the reading increased a bit too as radioactivity is random or spontaneous, so the background radiation can spike at times.

note : by an increase they dont mean a huge increase, just minor ups and downs as you could see in the graph. hence the best fit line was drawn.

how many marks u expecting???
70??

 

[kboss]

What did you guys get for the efficiency of the turbines ?

33.something

 

[shafayat]

What did you guys get for the efficiency of the turbines ?

25%

 

[Zeus]

yeah, same here . and which way would the statue move, anti-clockwise or clockwise ? I said clockwise, I wrote about stability.

 

[Zeus]

I got 33. % , not 25%.

 

[kboss]

yeah, same here . and which way would the statue move, anti-clockwise or clockwise ? I said clockwise, I wrote about stability.

i wrote anticlockwise and returning to equilibrium.....it was just a guess though

 

[Zeus]

And to get the half-life, you never have to subtract the back-ground radiation. You're suppose to multiply 52 x 1/2= t1 and again 52x1/4= t2. The mean average of t1+t2/2 = Half-life.

 

[shafayat]

I got 33. % , not 25%.

becuz u wrote in the denominator ...only the power LOSS .. u didnt add the USEFUL POWEROUTPUT to get the TOTAL POWER INPUT .... u just put the value from the mgh in this n left it like that !! but in the question its clearly stated ! TAKE THIS AS THE POWER LOSS / second !!!
so u will have to add the useful power to get the total power output

 

[kboss]

And to get the half-life, you never have to subtract the back-ground radiation. You're suppose to multiply 52 x 1/2= t1 and again 52x1/4= t2. The mean average of t1+t2/2 = Half-life.

i messed up that question and got 2.6 days which would be woefully wrong
still if i get 60+ i think and A* is likely since i don't think i lost more than 3 marks in p1 and hope to do well in p6

 

[Zeus]

becuz u wrote in the denominator ...only the power LOSS .. u didnt add the USEFUL POWEROUTPUT to get the TOTAL POWER INPUT .... u just put the value from the mgh in this n left it like that !! but in the question its clearly stated ! TAKE THIS AS THE POWER LOSS / second !!!
so u will have to add the useful power to get the total power output

You got it the other way around, you they gave you a %. Your total energy input was your mgh=E. You suppose to multiply that with the percentage to get the useful power output. You divide that by total energy input, and I guess it comes- 33.1 or 33.3 %. I forgot. What did majority get ?

 

[kboss]

You got it the other way around, you they gave you a %. Your total energy input was your mgh=E. You suppose to multiply that with the percentage to get the useful power output. You divide that by total energy input, and I guess it comes- 33.1 or 33.3 %. I forgot. What did majority get ?

i did 10400/something and multiplied it by a 100....
what abt the t-shirt question....it was all based on evaporation

 

[shafayat]

You got it the other way around, you they gave you a %. Your total energy input was your mgh=E. You suppose to multiply that with the percentage to get the useful power output. You divide that by total energy input, and I guess it comes- 33.1 or 33.3 %. I forgot. What did majority get ?

the total energy input was .. the loss + the useful power
they said mgh= loss /sec .. then u add the useful power !
then u get the total power output

 

[Zeus]

Yeah. The T-shirt question was easy I guess. More wind, more evaporation. The other one was folded, so less surface area.

 

[shafayat]

i did 10400/something and multiplied it by a 100....
what abt the t-shirt question....it was all based on evaporation

the Tshirt was an easy one ! all abt evaporation

 

[Zeus]

the total energy input was .. the loss + the useful power
they said mgh= loss /sec .. then u add the useful power !
then u get the total power output

Not sure man. Lets see what majority of the people got ?

 

[shafayat]

Not sure man. Lets see what majority of the people got ?

majority IN MY SCHOOL got 33.1%

 

[kboss]

Not sure man. Lets see what majority of the people got ?

my whole class got 33.something and my teacher said the answer would be the same when i asked him later on

 

[kboss]

majority IN MY SCHOOL got 33.1%

hw much u expectin?
65+?