Physics Paper1 M/J 2006 and O/N 2006

[1992]

Please can someone explain the M/J 2006: Q 12, 25, 27, 31 and 33
O/N 2006: Q 17, 18, 21 and 27 please!!

 

[mahad]

ok starting from nov/oct 06
q17 => efficiency = required output / input x 100. here the output is light. input total is 93 + 7 Joules. 7/100 x 100. gives you 7%.
q18 => efficiency of the locomotive is 80%. find out the voltage supplied. which is 80% of 25000V. now. for this voltage calculate the current. P=IV. 200A.
q21 => total pressure is because of the oil and the water. use formulae. 17.5 x 10^6 = 1000 x 9.81 x (2000-X) + 830 x 9.81 x X. (where capital X is the thing to be found)...comes out to be 1271.2m. rounded off to 1270m.

 

[mahad]

q27 => well they told you that slit separation is 500 times more than the line spacing of the grating. suppose the grating separation is T. so apply the formula used in diffraction grating to get lambda in terms of a. => dsintheta = nlambda. (d = T, theta = 30degrees, n = 1). so lambda = T/2. now use the fringe separation formulae. x = lambda x D / a. (we know a = 500T and lambda = T/2). so fringe separation comes out to be 1/1000 ie 1.o x 10^-3.

 

[mahad]

ok coming to may/june 06
q12 => mass of first truck is m and its velocity is 2v. it's momentum becomes 2mv. mass of second truck is 3m and its velocity is -v because it is coming in the opposite direction. after collision mass becomes 4m as both stick together and there speed let be V. as there momentum is conserved therefore momentum before collision = momentum after collision. so 2mv - 3mv = 5mV. V = -1/4v. they only asked about the magnitude of velocity (speed) which is 1/4v.
q25 => easy one. apply c=flambda to get lambda = 0.68m. now for phase difference apply distance between particles divided by lambda which comes out to 1/4. as the answer is in radians multiply this by 2pie. to get 1/2pie.
well lemme solve the other ones now =P

 

[mahad]

I'm a bit confused about 27. did 31 first.
well the direction is obvious it is from y to x because how the battery is connected. now find out time. q = I x t. q = 1.6 x 10-19 and I = 4.8A. T comes out to be 3.33 x 10-20. as it demands tha rate of flow which is 1/T. so inverse this to get 3x10^19. C option.