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Physics: Post your doubts here!

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sagar65265

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ShreeyaBeatz said:
View attachment 44307
What does this mean? Please explain. sorry for the two posts. I couldnt remove it :)View attachment 44307 View attachment 44307
Click to expand...

We have to look quite hard to get the answer - why does the current seem to prefer the train rather than the relay? Note that a relay should have a low resistance to ensure maximum current flowing through it (and this causes the electromagnetic effect that turns the switch on or off).

So if current prefers the train rather than the relay, then shouldn't the train have an even lower resistance than the relay?

This resistance is practically Zero, since the train is preferred over a relay coil.
Therefore, without the resistor, the current would just flow out of the positive terminal and back into the negative terminal, short-circuiting the circuit. So, to ensure this does not happen, a resistor is placed in series with the train connection (the tracks) which will dispense of most of the energy supplied by the battery whenever the train is on the track.

Hope this helped!
Good Luck for all your exams!
 
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sagar65265

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_Ahmad said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w08_qp_1.pdf

Q7,10
Click to expand...

When the stone is thrown and in the air, the only force acting on it is gravity, acting vertically downwards. Therefore, the net force F on the stone is also downwards and has a magnitude of (mg) Newtons.

By Newton's Second Law, since the net force F is downwards, the acceleration of the stone is F/m downwards. This translates to a downward acceleration of magnitude (mg)/m = g ms^-2 = 9.81 ms^-2.

There is no force on the stone in the horizontal direction, so the horizontal acceleration is zero, and the horizontal velocity is constant. Gathering our facts, we see that:

i) the stone has a constant downwards acceleration (a constant vertical acceleration, since the net force of gravity acting on the stone is constant), and
ii) the horizontal velocity of the stone does not change because there is no horizontal force component acting on the stone.

The only option that satisfies both these requirements is A.

10)
jumana94 has already answered this (3 years back!) at this link:

https://www.xtremepapers.com/community/threads/physics-mcq-help.8257/#post-111624

Thanks, jumana94 !

Good Luck for all your exams!
 
not.maria

not.maria

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Ahmed H. Al-Neel said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w11_qp_11.pdf
questions 4,26,29,30,32,37 really need help!
Click to expand...
for Q4 use trial and error method until the units on both sides of the equation are equal
L and a has units (m )while T has unit (s)
by using option B we get units on the right hand side equal to the left hand side
upload_2014-5-30_15-18-22.png

for q29
For a stationary wave in P there should be a node at the closed end and an antinode at the open end.For a wave to be formed in Q there should be an antinode at both ends.
length of P=35 cm
wavelength of given wave = 20 cm
so 35/20 = 1.75 lambda can fit in P. if you draw a wave 1.75 lambda long starting with a node you will find that it ends with an antinode so this means that a stationary wave would be formed in P
for Q 50/20 = 2.5 lambda would fit in it.
start by drawing an antinode at one open end and continue until you draw 2.5 lambda .u will find that an antinode also forms at the other end.This satisfies the condition for a stationary wave .hence you will get a stationary wave in Q as well
 
not.maria

not.maria

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Ahmed H. Al-Neel said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w11_qp_11.pdf
questions 4,26,29,30,32,37 really need help!
Click to expand...
for q37
find the current in the ammeter for each circuit diagram by assuming random values for emf and resistance.I took emf 6V and Resistance 12 ohm for each resistor
for A
the effective resistance will be 12+12=24 ohm
using V=IR , I comes 0.25 A
For B
the current does not pass through the second resistor but instead follows the pathway through the first resistor and the ammeter.
so we will take resistance of the first resistor only. R=12 V=6 so I comes as 6/12= 0.5A
for C
we need the current that passes through one resistor in the parallel combination only.
again R= 12 V=6 so I comes as 0.5 A
in D
the current that passes through the ammeter is the current that passes through the whole circuit.the resistors are in parallel combination so
The effective resistance is
1/effective resisatnce= 1/12 + 1/12
=6 ohm
I=V/R =6/6 =1 A
this is the largest ammeter reading so D is the ans.
This is how i solved the question .I hope it helped
 
Thought blocker

Thought blocker

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Ahmed H. Al-Neel said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_w11_qp_11.pdf
questions 4,26,29,30,32,37 really need help!
Click to expand...
not.maria said:
for Q4 use trial and error method until the units on both sides of the equation are equal
L and a has units (m )while T has unit (s)
by using option B we get units on the right hand side equal to the left hand side
View attachment 44333

for q29
For a stationary wave in P there should be a node at the closed end and an antinode at the open end.For a wave to be formed in Q there should be an antinode at both ends.
length of P=35 cm
wavelength of given wave = 20 cm
so 35/20 = 1.75 lambda can fit in P. if you draw a wave 1.75 lambda long starting with a node you will find that it ends with an antinode so this means that a stationary wave would be formed in P
for Q 50/20 = 2.5 lambda would fit in it.
start by drawing an antinode at one open end and continue until you draw 2.5 lambda .u will find that an antinode also forms at the other end.This satisfies the condition for a stationary wave .hence you will get a stationary wave in Q as well
Click to expand...
26)
∆L is basically compression.
L = Original length
When compression increases, original length decreases - fact - hence, inverse proportionality.

You can also prove it like this:
Strain = extension/original length => e / L
Compression = 1/e
Therefore, strain = 1/eL
When you look at this equation, you'll see that 1/e (compression ∆L) and L are inversely proportional.

30)
Waves have to superpose for interference pattern to be produced at RS the waves have not been yet superposed.
If you dont get me, here is something elaboration :¬
At first the waves have to be produced, when two waves meet they superpose but at line XY there is maximum of interference pattern compared to RS beacause waves have to meet first, so answer is C

32)
resultant force is zero because it rotates at a constant speed because and anti clockwise because E is downward so downward is negative so it repels it and it became anti clockwise, C

37)
Above post
 
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papajohn

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Which graph represents the motion of a car that is travelling along a straight road with a speed
that increases uniformly with time?
upload_2014-5-30_14-25-21.pngupload_2014-5-30_14-25-21.png
How the the hell A is correct. C should be correct it beacause Question say "moving in straight line" which mean positive s.Why the ** A is correct?:mad:
 
Thought blocker

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papajohn said:
Which graph represents the motion of a car that is travelling along a straight road with a speed
that increases uniformly with time?
View attachment 44342View attachment 44342
How the the hell A is correct. C should be correct it beacause Question say "moving in straight line" which mean positive s.Why the ** A is correct?:mad:
Click to expand...
We know that V is proportional to A so V will be constant as A is constant :)
 
Ahmed H. Al-Neel

Ahmed H. Al-Neel

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Thought blocker said:
26)
∆L is basically compression.
L = Original length
When compression increases, original length decreases - fact - hence, inverse proportionality.

You can also prove it like this:
Strain = extension/original length => e / L
Compression = 1/e
Therefore, strain = 1/eL
When you look at this equation, you'll see that 1/e (compression ∆L) and L are inversely proportional.

30)
Waves have to superpose for interference pattern to be produced at RS the waves have not been yet superposed.
If you dont get me, here is something elaboration :¬
At first the waves have to be produced, when two waves meet they superpose but at line XY there is maximum of interference pattern compared to RS beacause waves have to meet first, so answer is C

32)
resultant force is zero because it rotates at a constant speed because and anti clockwise because E is downward so downward is negative so it repels it and it became anti clockwise, C

37)
Above post
Click to expand...
Thank you sooooo sooo much idk how to thank you enough you helped me aloooot
 
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