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Physics: Post your doubts here!

princessnoor

princessnoor

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chishtyguy

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Thought blocker said:
5)
IDK

7)
At R jumper will be at rest, coz no velocity
At Q accn is zero as Q is the maximum height gained by jumper.

8)
Short answer, because the time taken with each speed is different.

Let's do the math behind this - suppose the distance traveled with both speeds is denoted by "s".
Suppose the time taken at 600 kmph = t(1).

Then, since Speed = Distance/Time, we can write

600 = s/t(1)
So that
t(1) = s/600

Similarly, let's do the same for the other speed. The distance traveled is still "s", the speed = 400 kmph, and the time taken to traverse this distance = t(2). So:

400 = s/t(2)
So that
t(2) = s/400

The average speed is the total distance traveled dividing by the time taken (the average velocity is different - it is equal to total displacement divided by time taken).
= (Total Distance traveled)/(Time taken to cover that distance).

Since the plane travels a distance "s" in one direction and returns the same distance "s", the total distance traveled = s+s = 2s.

The time taken = t(1) + t(2) = s/400 + s/600 = 3s/1200 + 2s/1200 = 5s/1200 = s/240

Therefore, the average speed = 2s/(s/240) = 480 kmph = C.

11)
Mass of α = 6.6 x 10⁻²⁷
Speed of α = 1.5 x 10⁷
No. of α per sec = 50000 in area of 0.0001 m²
Use P = f / A
P = ma / A
mass of 50000 = 50000 * 6.6 x 10⁻²⁷
acceleration = V / t Where V = 1.5 x 10⁷ and t = 1
P = [ (50000 * 6.6 x 10⁻²⁷) x 1.5 x 10⁷ ] / 0.0001
P = 4.95 x 10⁻¹¹ ≈ 5 x 10⁻¹¹

39)
using a double thickness foil
Theory based answer, come on
  1. After voltage passes through some resistance it will decrease
  2. The higher the resistance the greater the decrease in voltage
-->So it will decrease less after passing through 2 ohm than when passing through 4 ohm
Hence it is D
Click to expand...
Q5 is .6% as Volume 4/3 (Pie) r^3
so cube will become the co-efficient as 3( l'/l)
Percentage uncertainity in Volume is v'/v x100 = 3(l'/l) x 100
that is .6%
 
Asad Moosvi

Asad Moosvi

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crazytaylorfanXD said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_11.pdf

qs 5????
Click to expand...

When you add or subtract quantities, you add their absolute uncertainties.

d2 = 385
d1 = 115
uncertainty in d2 = 1
uncertainty in d1 = 1
delta d = 385 - 115 = 270
absolute uncertainty in delta d = uncertainty in d1 + uncertainty in d2 = 2

t2 = 3.5
t1 = 1.5
uncertainty in t2 = 0.02
uncertainty in t1 = 0.02
delta t = 3.5 - 1.5 = 2.0
absolute uncertainty in delta t = 0.02 + 0.02 = 0.04

fractional uncertainty in delta t = 0.04 / 2
fractional uncertainty in delta d = 2 / 270

You just add the fractional uncertainties.
 
chishtyguy

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Wolfgangs said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w08_qp_1.pdf
Q1, 5 and 10 pleaSE
Click to expand...
Q1 answer is C
as c= Wavelenght/ time
t=wavelenght/c= 2x10^15
waves in one sec is frequency so f= 1/2x10^15= 5x10^14
Q5
Well I got it wrong at first... But it's just
look at the actual true current .8 and look at faulty ammeter its also .8, so both the readings are closest
Q10
M not completely sure of the formula but in A's We use the formula
initial + final velocity of sphere 1= initial +final velocity of sphere 2
by arranging them we will have
u1+v1= -u2 + v2
rearrange them
u1+u2=v2- v1
About the formula Thought blocker M I correct???
 
chishtyguy

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Menu Mendz said:
Could someone help me in Q's 10,38 and 39 of this paper
Oct 2012 paper 12
Thanks in advance!!!
Click to expand...
For question no 10 it's D
its not B, As velocity vertical component is continuously changing while horizontal component is Constant
Its not A, Veloicity can't be zero because object has not yet landed
Its not C, Although at maximum height vertical component is zero but there is a horizontal component so Velocity can't be zero..
D correctly represents it

For q 38 it's B
use the formula R/R+5000 x 1.5
At R = 1000, V= .25V
R=1000000, V= 1.49~1.5
look at graph B's max and Min Val

Q 39 its C
C as helium nuclei has only neutron and proton
Nucleon has Proton and neutron
so as Alpha particles increases number of nucleons decreases
 
Thought blocker

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Asad Moosvi said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w10_qp_13.pdf

Question 31 and 37.
Click to expand...
31)
The total resistance of the cable is 8 ohms. The cable is 800 meters long since that's the distance between the power supply and the relay and there are 2 wires in the cable. 0.005 ohms per m means in one wire the resistance is 0.005 ohms x 800 = 4 ohms. So total resistance is 2 x 4 = 8 ohms.
Add the resistance of the wires to the resistance of the relay. Relay's resistance is R = V/I = 16/0.6 = 26.7 ohms. (26.7 + 8)
To find the output voltage = IR = 0.6 x (26.7 + 8) = 20.82 and the answer is C.
We are treating the relay and wires as one unit. The current through wires does not change and so we can plug the 0.6 amps of the relay into the V=IR formula.
It just seems like it's complicated but it really isn't. Try looking at it in a simplified way.

37)
1/30 + 1/10 = 4/30 now inverse it you get 7.5
so B :)
 
L

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Aoa everyone.
Im REALLY stuck on this one specific type of question in all my pastpapers and they are the diffraction grating ones. I havent even gotten a single one right yet and I would EXTREMELY appreciate if someone could just explain 2 of these so I'll understand the rest myself. :) JazakAllah
Q. 30 from O.N/2012
Q. 27 from O.N/2010
 

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Asad Moosvi

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Thought blocker said:
31)
The total resistance of the cable is 8 ohms. The cable is 800 meters long since that's the distance between the power supply and the relay and there are 2 wires in the cable. 0.005 ohms per m means in one wire the resistance is 0.005 ohms x 800 = 4 ohms. So total resistance is 2 x 4 = 8 ohms.
Add the resistance of the wires to the resistance of the relay. Relay's resistance is R = V/I = 16/0.6 = 26.7 ohms. (26.7 + 8)
To find the output voltage = IR = 0.6 x (26.7 + 8) = 20.82 and the answer is C.
We are treating the relay and wires as one unit. The current through wires does not change and so we can plug the 0.6 amps of the relay into the V=IR formula.
It just seems like it's complicated but it really isn't. Try looking at it in a simplified way.

37)
1/30 + 1/10 = 4/30 now inverse it you get 7.5
so B :)
Click to expand...

In question 31, how do you know the two wires inside are in series? They could be in parallel too, the question doesn't specify.
 
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