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|dw:1356509438621:dw|

concepts of physics?

??

nthin i thot it was from hc verma
well
i think i missed smthin fk=5N?
why wud they seperate?

pseudo force i'd say..

and i dont know from which book this ques came from,,it was asked in a test..

yup and wat's the acceleration?
10*1

how ?

shouldnt it be
30 -fk = 30 - 5 ?

=25

i dont think fk counts initially
they both move as a single body

opps sorry u r right
nd u almost got it

well i'll show you my attempt..just that i didnt get the right ans..

find the independant acc's of both?
and find the replative acc
and use that goddamn formula

wait, can you confirm to me if the normal reaction acting on the block is 1*10N or (1+2)*10 N ?

idk...gime sm time i feel giddy

i still find something fishy in my solution.. hmm :|

how do you say force on block 1 is 10 N?
shouldnt the pseudo force be 30 N ?

as far as i kno pseudo is ma

ohh
u from fiitjee?

no buddy,, :|

hmmm ..nevermind,,thanks for trying sir! :)

|dw:1356521627848:dw|

So, accleration of the block with respect to the plank = -25/1 = -25ms^2

Now,
s=ut+1/2 at^2
2=0+1/2 25 t^2
t^2=100
t=10seconds

When the block starts to move the maximum friction acts on it i.e.5N
Then we draw the free body diagram as shown in the file attached. Note that we work in the frame of the plank because it is easier. Pseudo force is given by "ma". Where m is the mass of the body in concern(i.e. in this case 1kg) and "a" is the acceleration of the frame(i.e. the plank). We get the free body diagrams for plank and block as shown.
Eqn of motion for plank is 30-5=2a giving a=12.5m/s/s
Eqn of motion for block is 1*a-5=1*A where A is the acc of the 1kg block
Inserting the value of "a" gives A=7.5m/s/s
Length of plank is 2m
Using 2nd eqn of motion we get time to cover 2m =0.73s(approx)
***DO TELL THE CORRECT ANSWER PLEASE**

relative to the plank..

Yes, because we are working in the frame of the plank.

i understand this concept a lot better now..thanks..

acceleration w.r.t. ground can be found out as a-A=12.5-7.5=5

.where a and A are the magnitudes. we used - sign because they point in opposite directions.

yep..again,,thanks a ton! :)

you are welcome!!