Physics Pp:3-Variant 2- Discussing Answers!!

[ZiadAmr]

must mention the type clockwise or anti clockwise.

it is anti clockwise by the way.
when we were all young we played with toys like these, funny we should sit for an exam with a question regarding one too.

Yeah i said rotates back anticlockwise

 

[wooowooowoo]

but you have to deduct background radiation which was 14
making your inital count 52-14= 38

divide that by 2 = 19
add background radiation again 19+14= 33
now find how long it took to reduce to 33 counts
should be 1.6 I guess

but I wouldnt know, i forgot to add back the background radiation. but it will not exceed 2.5 days I guess, there's always a range.

If you have to add the background radiation again (at the end) so there is no need of reducing it in the starting, right ?

 

[Dandelion]

no did you read part 2 of question (a)?
when there is the weight thingy at the tail, the centre of mass is at the pivot.

im not suree. but logically if theres a seesaw with the centre of mass at the centre, then when you place an object that makes the seesaw rotates, the centre of mass still doesnt shift isnt it. /

 

[omglaigcse]

im not suree. but logically if theres a seesaw with the centre of mass at the centre, then when you place an object that makes the seesaw rotates, the centre of mass still doesnt shift isnt it. /

but the question did state there that the centre of mass shifts to the pivot when there is a weight at the tail.
so that means there's no anticlockwise moment at all, so there's no way for it to move anticlockwise. should be clockwise

 

[Chucky]

If you have to add the background radiation again (at the end) so there is no need of reducing it in the starting, right ?

you deduct to find ONLY source radiation, then you divide by two for ONLY source halflife
you only need to add background radiation back so that you can find out the time taken from the graph, becuase the counts per minute is with the background radiation as well.


sorry if my explanation isn't all too convincing, but trust me, that is the way to do it.
if you divide directly you get 26 counts per minute instead of 33.

 

[Dandelion]

but after you get 19 counts per minute you have to add the background radiation again because remember, the graph shows counts/minute INCLUDING background radiation

so you add 14 to 19 and you get 33
number of days to reach 33 is 1.6 days

and the bulb question, i got the answer as 8 or 9 but unfortunate for me, i solved it after the paper was taken......... no time for writing it down
i could only deduce the total resistance of the circuit if the current was 0.9A, which is 266.67 ohms, after that the teacher snatched my paper
(p.s. i left this question for the last, everything else i finished)

how do you know that the background radiation is exactly is 14 ?? it varies.. so i dont think making any calculation with the background radiation is valid. all i did was just read from the graph and i got 2.6 days. in any textbook, when they show how to find the half life time, they just read from the graph tho. well i dont know, this is my point of view

 

[Chucky]

but the question did state there that the centre of mass shifts to the pivot when there is a weight at the tail.
so that means there's no anticlockwise moment at all, so there's no way for it to move anticlockwise. should be clockwise

the question states that the weight which caused it to tilt left was not applied anymore.

think of this, you pull the tail and it rotates clockwise, but you LET GO, what happens? does it still keep rotating clockwise? no!
because then the clockwise moment decreases when you let go, becoming equal to anticlockwise moment again ( as original)
and it comes to equilibrium with an anticlockwise rotation.

try playing with a balancing toy, you'll see.

 

[wooowooowoo]

you deduct to find ONLY source radiation, then you divide by two for ONLY source halflife
you only need to add background radiation back so that you can find out the time taken from the graph, becuase the counts per minute is with the background radiation as well.


sorry if my explanation isn't all too convincing, but trust me, that is the way to do it.
if you divide directly you get 26 counts per minute instead of 33.

If that is correct then I've just lost 3 more marks. Woohoo

 

[omglaigcse]

how do you know that the background radiation is exactly is 19 ?? it varies.. so i dont think making any calculation with the background radiation is valid. all i did was just read from the graph and i got 2.6 days. in any textbook, when they show how to find the half life time, they just read from the graph tho. well i dont know, this is my point of view

it's not always about the textbook, it's how you apply and relate your knowledge cause this is physics.
and there's a reason why the question was 4 marks

 

[Chucky]

how do you know that the background radiation is exactly is 19 ?? it varies.. so i dont think making any calculation with the background radiation is valid. all i did was just read from the graph and i got 2.6 days. in any textbook, when they show how to find the half life time, they just read from the graph tho. well i dont know, this is my point of view

you didn't understand background radiation is 14
you deduct that from initial counts which was 52 making the SOURCE ONLY COUNTS 38

divide 38 by 2 and THEN YOU GET 19.
but you have to add back background radiation as your graph includes that in it's readings.

 

[omglaigcse]

the question states that the weight which caused it to tilt left was not applied anymore.

think of this, you pull the tail and it rotates clockwise, but you LET GO, what happens? does it still keep rotating clockwise? no!
because then the clockwise moment decreases when you let go, becoming equal to anticlockwise moment again ( as original)
and it comes to equilibrium with an anticlockwise rotation.

try playing with a balancing toy, you'll see.

no. ok i'll use your example.
if there's a heavy weight on the toy on one side, do you really think it will stay? and obviously it wouldnt go the other way. the weight is on the right side and obviously it will move clockwise till it's right at the bottom of the pivot.

and i'll explain to you technically.
moment = force x PERPENDICULAR distance from pivot
you see, the mass, which is at the pivot is 0 distance from the pivot cause it's right there. so there is no anticlockwise moment.
there is distance and force on the right side, so there is clockwise moment.
so it moves clockwise.

makes sense?

 

[wooowooowoo]

no. ok i'll use your example.
if there's a heavy weight on the toy on one side, do you really think it will stay? and obviously it wouldnt go the other way. the weight is on the right side and obviously it will move clockwise till it's right at the bottom of the pivot.

and i'll explain to you technically.
moment = force x PERPENDICULAR distance from pivot
you see, the mass, which is at the pivot is 0 distance from the pivot cause it's right there. so there is no anticlockwise moment.
there is distance and force on the right side, so there is clockwise moment.
so it moves clockwise.

makes sense?

No. :/

 

[omglaigcse]

No. :/

it's sort of logic right. you hold a toy with a heavy thing on the right side.
clearly it will fall downwards, and to do so, it moves clockwise.

 

[AAnsarii]

24 hours have passed so... lets start discussing!
1) Please someone tell me what did you get for the Bulb question?? I didn't have time to solve the Qs so i just wrote the first number that came to my mind..4
2) When the magnet enters the coil, the force induced is upward or downward ? I didn't know it so i guessed it and wrote downward!
3)What did you get for the radioactivity life?? I got 1.6 days
4)The question about the tidal thingy, the water goes left or right ?? (i didn't even know what the question was about)
5) When drawing the red ray (reflection and Refraction) how do you do it ? I traced the reflection part over the blue one, but didn't do the refraction part
6) The gate where NOR, & the two ones are Not and OR Right ?? The Y had 0 (Low) and Z had 1 (High)

That's all i have to ask for now.. Note that i left some questions un answered due to time limit !!

2) i didnt noe, i rote out of d pg
3) i think i got 2.6 days
4) it goes 4m high to low, dont remmbr left/rite.

 

[wooowooowoo]

it's sort of logic right. you hold a toy with a heavy thing on the right side.
clearly it will fall downwards, and to do so, it moves clockwise.

But the toy isn't kept in the middle, it's tilted towards the left so it'll go back anti-clockwise, no?

 

[omglaigcse]

But the toy isn't kept in the middle, it's tilted towards the left so it'll go back anti-clockwise, no?

it's tilting to the right. the right is the lower side, the tail with the weight hanging on it. it's tilting to that side, and there's something heavy on it. surely it will move that way

 

[Dandelion]

it's sort of logic right. you hold a toy with a heavy thing on the right side.
clearly it will fall downwards, and to do so, it moves clockwise.

but remember, the toy is lighter than the bird

 

[wooowooowoo]

it's tilting to the right. the right is the lower side, the tail with the weight hanging on it. it's tilting to that side, and there's something heavy on it. surely it will move that way

Wasn't it stable in the first diagram and then in the second diagram it was tilting towards the left with the weights added onto the tail ?

 

[omglaigcse]

but remember, the toy is lighter than the bird

what toy and bird. the toy is the bird.

 

[omglaigcse]

Wasn't it stable in the first diagram and then in the second diagram it was tilting towards the left with the weights added onto the tail ?

it was stable because there was no weight and the centre of mass was at M.
but when there they hang the weight at the tail, the centre of mass is at the pivot.

then they said they tilt the bird in that position, so what happens after that.