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Physics: Post your doubts here!

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upload_2015-6-9_15-52-18.png
Why C?
The current flows from left to right so to increase the current accross the sliding contact, shouldn't it be D??
 
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Resistance = resistivity * (length/x-sectional area)
length is halved and area is doubled so resistance is 1/4th of the original.
Screen Shot 2015-06-09 at 4.15.43 PM.png

but then why isn't this concept applicable here? here the ans is C, why ? :S how is it different?
 
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HELP :(

Ans is C
Driving force = ma = 1800 * 2 = 3600N
Tension in first cable from left = T0
Motion of powered vehicle:
3600 - T0 = 200(2)
T0 = 3200
Motion of cart 1:
T0 - T = 400(2)
T = 2400N

HELPPP

Correct answer is C.

Moment due to weight = 0.1 * 10 * 9.81 = 9.81 clockwise
Moment due to pulley = 0.02*9.81*60 = 11.77 anti cw
difference is 1.962 anti cw, so we need 1.962 in cw direction, which we get by placing 50g on the 44cm mark.
 
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