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Physics: Post your doubts here!

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Look the question has itself given you the answer "constant velocity" What does this mean? Forces are at equilibrium or are balanced thus look for such a diagram which would follow the course of a complete triangle. Look at the arrows. Every arrow should lead to a complete triangle. Idk how to explain it but thats the best I could do. :/
 
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Current is unchanged because it's connected with the fixed resistor which will have a different reading as compared to the one with the variable one as they're connected in parallel and the reading of the voltmeter decreases because there's an increase in resisitance leading to a decrease in the current in this part of the circuit. thus reducing the Pd as well.
Please could you explain why the current is unchaged though as I don't understand that one? Like the total resistance of the circuit decreases, so the current increases. The ratio of the resistances at the junction would increase so more current would flow to the fixed resistor at the top so shouldn't ammeter reading increase?
But then why is it unchanged?
 
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upload_2015-6-6_20-11-10-png.54683
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Why not B?
 
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Just asking, How do you guys post the screenshot thingy? I don't usually get answers if I post the whole paper and ask for a certain question. :(:mad::confused:
Either use the snipping tool if you have on your laptop. Using that it automatically copies the image that you have cropped and then past it on here.
Or if you don't have the tool then just take a screenshot of the question you want and paste it here :)
 
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First find the resistance of the 2 wires: Resistance is 0.005 ohm per m, the length of a wire is 800m
R for 1 wire= 800*0.005=4 ohm
Total R for cable (2 wires)= 4*2=8
Current in circuit= 0.6A
PD across cable= 0.6*8=4.8
Emf= 4.8+16=20.4V
Thanks a lot guys. :)
 
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Use vertical motion to find the time (time to travel vertical distance = time to travel horizontal distance)
s = 1.25 , a = 9.81 , u = 0
using s = ut + 1/2 at^2
you get t = 0.5048...

Then use horizontal motion
s = 10 and t = 0.5048...
speed = distance / time (since there is no acceleration in horizontal motion and speed remains the same throughout)
this will give v = 19.8.... which is roughly 20.
 
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I get it a bit:D, What I still don't get is why wud the pattern be like up down down up.. :p but it s okay thanks a lot ! :)
Let me just make a last attempt :)
Since it's travelling at 4m/s, the wave must travel, in 0.125s, 0.5m. Let's look at the wave step by step: (s is how much wave moved horizontally from initial position)

t=1, (s=4)
QuickMemo+_2015-06-06-22-47-30.png

x hasn't moved yet. It's displacement = 0

t=1.125, s=4.5
QuickMemo+_2015-06-07-10-30-24.png
x has moved down. It's displacement = -1

T=1.25, s=5
QuickMemo+_2015-06-07-10-31-17.png
At this moment, displacement is still -1, but within this instance, it's gonna go all the way up.

T=1.375, s=5.5
QuickMemo+_2015-06-07-10-33-53.png
x has moved up, displacement = +1

T=1.5, s=6
QuickMemo+_2015-06-07-10-35-09.png
x is at +1 but is gonna move down in this very instance.

Now you may plot time against displacement. You'll see that it matches graph of B
 
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Please could you explain why the current is unchaged though as I don't understand that one? Like the total resistance of the circuit decreases, so the current increases. The ratio of the resistances at the junction would increase so more current would flow to the fixed resistor at the top so shouldn't ammeter reading increase?
But then why is it unchanged?
Look at the position of the ammeter. It's connected next to the fixed resistor and the fixed resistor is parallel to the variable one therefore the currents have to be different in both the loops i.e the ammeter is only giving you the current across the fixed resitance.
 
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Look at the position of the ammeter. It's connected next to the fixed resistor and the fixed resistor is parallel to the variable one therefore the currents have to be different in both the loops i.e the ammeter is only giving you the current across the fixed resitance.
But then why doesn't the current through the fixed resistor change? Like the current is different in both loops
Now the resistance of the bottom loop is changed so it increases right
The top loop resistance stays the same
So the ratio of the 2 resistances in the 2 loops increases
The current divides in the inverse of the ratio of this resistance
So the current in the top loop would increase right? Like accross the fixed resistor... so wouldn't ammeter reading increase? :/
 
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But then why doesn't the current through the fixed resistor change? Like the current is different in both loops
Now the resistance of the bottom loop is changed so it increases right
The top loop resistance stays the same
So the ratio of the 2 resistances in the 2 loops increases
The current divides in the inverse of the ratio of this resistance
So the current in the top loop would increase right? Like accross the fixed resistor... so wouldn't ammeter reading increase? :/
No! See you can't just change the resisitance of the fixed resistance if the current flowing through it is the same as it was before. Ratio of the resisitances does not increase in both of the loops. How can it? You shoud treat these loops seperately as seperate circuits. The main thing is the position of the ammeter, the resistance through it has to remain the same. If the ammeter was connected with both of the resisitors your theory would've been right but these are seperate two loops with seperate currents. Idk how to explain it. :/
 
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No! See you can't just change the resisitance of the fixed resistance if the current flowing through it is the same as it was before. Ratio of the resisitances does not increase in both of the loops. How can it? You shoud treat these loops seperately as seperate circuits. The main thing is the position of the ammeter, the resistance through it has to remain the same. If the ammeter was connected with both of the resisitors your theory would've been right but these are seperate two loops with seperate currents. Idk how to explain it. :/
Oh ok! So if the ammeter was positioned say between the two loops , then the reading would decrease?
 
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Let me just make a last attempt :)
Since it's travelling at 4m/s, the wave must travel, in 0.125s, 0.5m. Let's look at the wave step by step: (s is how much wave moved horizontally from initial position)

t=1, (s=4)
View attachment 54723

x hasn't moved yet. It's displacement = 0

t=1.125, s=4.5
View attachment 54724
x has moved down. It's displacement = -1

T=1.25, s=5
View attachment 54725
At this moment, displacement is still -1, but within this instance, it's gonna go all the way up.

T=1.375, s=5.5
View attachment 54726
x has moved up, displacement = +1

T=1.5, s=6
View attachment 54727
x is at +1 but is gonna move down in this very instance.

Now you may plot time against displacement. You'll see that it matches graph of B
I got it !! :ROFLMAO:(y)(y)
JazakAllah
 
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Q.P http://maxpapers.com/wp-content/uploads/2012/11/9702_w12_qp_13.pdf
M.S http://maxpapers.com/wp-content/uploads/2012/11/9702_w12_ms_13.pdf

Can someone please explain Q 25?

And for Q 38, I get how gamma radiation will not be stopped by a few millimeters of lead, but inst alpha radiation absorbed by a few centimtres of air (1cm-3cm) ?
The weight of the man is supported by the 2 cables. Tension in 1 cable= (80*9.81)/2 = 392.4N
Stress= 392.4/ 1/4*3.142* 0.005^2
Strain= 0.001/10
E=2.0*10^11 Pa
 
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