aasan Q but it seems ive forgotten even laws of motion :((

I CAN TELL U IN WORDS(PLZ TRY TO UNDERSTAND....AS KEYS NOT WORKING).

U NEED TO MAKE FBD OF BOTH.IN FBD OF B THERE WUD BE FRICTION DUE TO A N DUE TO GROUND TOWARDS LEFT.SO FOR CONSTANT VELO. NET ACCELERATION SHOULD BE ZERO.

SO,FRICTION(BLOCKS)+FRICTION(GROUND)=P
I.E. P=SIXTEEN NU=FOUR N

GOT IT??????

ASHISH,DID U GET IT???????????

dude read ques. properly.where is it mentioned that A shud go with constant velocity!!!!!!!

first one i think john answered

for the second one the block A if kept intect will face kinetic friction as then there will be relative motion

thus we have

P-4μ-(4+8)μ=0

thus P=16μ

for the third one see that if B moves to the right then A will move to the left and thus there will be again kinetic friction ..

and as B will move with constant velocity it will face kinetic friction in the bottom surface too

further as B will move with constant velocity A will to and thus both will remain in equillibrium

thus we have T=4μ

P=T+4μ+(4+8)μ

but the first one should have answer as 3N

rohan for first Q,
Consider a force P=4 N acts on B
then consider the forces on A
IT is 1 N towards the right and hence its acceleration is 1/0.4 = 2.5m/s² hence the block A will slip over B and friction will cahnge direction and act backward on A and forward on B .. So, then B will again acclerate (it wont go with constnat velocity)

I was thinking to take A and B as the whole system...
If u do that then P=3N which i think is valid.. Consider that P=3.000001 N then accleration of B is very little (A will provide only 0.000001 N towards left) and similarly dut to the very little force acting on A it wont slip on B ..

which one is correct?

as i mentioned P=3N ...

it is because as B will move with constant velocity A also has to as it doesnt slip on it

so the friction acting on A should be zero thus P=μ(4+8)=3N

so you havent forgotten laws of motion ... :)

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surely NEWTON will suicide after reading this justification for 3N

i haven't forgot LOM.ans. is 4N only.