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Physics: Post your doubts here!

The Godfather

The Godfather

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Wolfgangs said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s13_qp_11.pdf

Q17, 18, 24,29,35,37
Click to expand...
Q17
since it's the bottom of the ball that hits the ground first, we have to consider the bottom of the ball
by law of conservation of energy,kinetic energy at bottom=potential energy at top
mx9.81x.72=0.75J
m=.11kg
second time,
.11x9.81x.37=ans
use the exact mass of the ball and you would end up with b as the answer
Q18
Snowysangel said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s13_qp_11.pdf q18
Click to expand...
Power = Energy / time.
Power = ( 0.5 * m * v^2 ) / t
Power = ( 0.5 *(rho * volume)* v^2) / t
Power = ( 0.5 *(rho * area * length)* v^2) / t
Power = (0.5 *(rho * area) * v^3)
Power = 1300kW
Q24
We know that intensity indirectly proportional to area and directly proportional to the square of the amplitude.
Dividing area by 3 causes the power per unit area(intensity)to increase by a factor of 3 and increasing the amplitude by 2 causes the intensity to increase by a factor of 4
so, (4x4)P=12P
the other 2 u will have 2 give me some tym
Q35
v1 = 600 / (600+3000/7) * 3 = 1.75V
v2 = 3000/7 / ( 3000/7 +600) * 3 = 1.25V
v = v1 - v2 = 0.5V
35.png
 
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Ahmed H. Al-Neel said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s09_qp_1.pdf
questions 10,15,18
Click to expand...
Q10
kinetic energy remains conserved,
initial = final
since its a stationary body, initial kinetic energy = zero
if velocity of m is v, then velocity of 2m has to be such that sum of momentum remains zero.
therefore,
so velocity of 2m is -v/2 ( negative 'cause its in the opposite direction)
you can check, mv + (2m)(-v/2) = 0
now, [ 1/2(m)(v^2) ] / [ 1/2(2m)(-v/2)^2]
it becomes 2/1.
Q15
if the depths of water are equal by the end then the gain in height of water in the second tank should be h/2.
since the tanks are identical each tank would have equal volumes so the mass of water that has moved to the other tank should be m/2. since mass is directly proportional to volume provided density is constant. And density IS constant since its water.
Now PE=( m/2)(h/2)g
=mgh/4
Q18
pressure = hdg. But here h is 2h since on one side liquid rises by h and another side liquid falls by h.
 
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Student12 said:
Question 26,30 http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s12_qp_12.pdf
Click to expand...
Q26
Reflected distance = 2 times the orignal so, 300m
time = distance / speed
time = 300 / 3 * 10^8 = 1µs
Q30
Its a standing wave, so the 33cm is the distance between two nodes. The wavelength thus becomes 0.66m. F = 330/0.66 = 500, T = 1/500 = 0.002s = 2m.
so it means wave should be completed in 4 blockss as the time base is 0.50ms/cm isiliye B
 
Ahmed H. Al-Neel

Ahmed H. Al-Neel

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The Godfather said:
Q10
kinetic energy remains conserved,
initial = final
since its a stationary body, initial kinetic energy = zero
if velocity of m is v, then velocity of 2m has to be such that sum of momentum remains zero.
therefore,
so velocity of 2m is -v/2 ( negative 'cause its in the opposite direction)
you can check, mv + (2m)(-v/2) = 0
now, [ 1/2(m)(v^2) ] / [ 1/2(2m)(-v/2)^2]
it becomes 2/1.
Q15
if the depths of water are equal by the end then the gain in height of water in the second tank should be h/2.
since the tanks are identical each tank would have equal volumes so the mass of water that has moved to the other tank should be m/2. since mass is directly proportional to volume provided density is constant. And density IS constant since its water.
Now PE=( m/2)(h/2)g
=mgh/4
Q18
pressure = hdg. But here h is 2h since on one side liquid rises by h and another side liquid falls by h.
Click to expand...
thank you sooo sooo much!
 
The Godfather

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H

huh

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http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s10_qp_11.pdf
Really need
Asad Moosvi said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w12_qp_12.pdf

In question 26, why is the answer D?

The breaking force isn't the same for both. There's a minor difference.
Click to expand...
The first curve is brittle, the second one isn't.
The second one doesnt obey Hooke's Law.
The first one is elastic not plastic, because force is proportional to extension.
The last one is the answer because both curves have equal peaks. Peak = Ultimate tensile stress.

Hope this helped.
 
A

Ahmed Aqdam

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Asad Moosvi said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w11_qp_12.pdf

Questions 8, 10, 23 and 28 please! :)
Click to expand...
8: The velocity is constant for the first part and the second part but both are different. So acceleration is not constant. Also, there is no evidence that speed is zero at the start so B is wrong. Its not a straight line so distance is not proportional. Speed changes so D.

10: At X, sand is stationary and truck is moving so when they stick together the speed decreases.
At Y, sand also leaves with some speed and as the total mass remains same, the speed will not change.

23: Elastic potential or strain energy is calculated by area under force-extension graph. This is greatest in B.
 
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