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a block of mass 1kg is placed on a plank of mass 2kg, length of plank = 2m. Coefficient of friction between plank and block is 0.5 and the round on which the plank is kept is smooth.
A constant force F=30N is applied on the plank; the time after which the block separates from the plank =?
 one year ago
 one year ago
a block of mass 1kg is placed on a plank of mass 2kg, length of plank = 2m. Coefficient of friction between plank and block is 0.5 and the round on which the plank is kept is smooth. A constant force F=30N is applied on the plank; the time after which the block separates from the plank =?
 one year ago
 one year ago

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shubhamsrgBest ResponseYou've already chosen the best response.0
dw:1356509438621:dw
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
concepts of physics?
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
nthin i thot it was from hc verma well i think i missed smthin fk=5N? why wud they seperate?
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
pseudo force i'd say..
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
and i dont know from which book this ques came from,,it was asked in a test..
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
yup and wat's the acceleration? 10*1
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
shouldnt it be 30 fk = 30  5 ?
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
i dont think fk counts initially they both move as a single body
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
i see,,i didnt consider that.. anyways, how does it matter? the question will begin only when the block starts moving..
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
i mean the solution will begin* also, fk isnt high enough relative to the force, so shouldnt it start moving at t=0 only ?
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
opps sorry u r right nd u almost got it
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
well i'll show you my attempt..just that i didnt get the right ans..
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
find the independant acc's of both? and find the replative acc and use that goddamn formula
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
wait, can you confirm to me if the normal reaction acting on the block is 1*10N or (1+2)*10 N ?
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
wat's block 1? anyways i think i understand ur confusion well i guess it is 10 but u jus need to find fk....and draw fbd with the horizontal forces
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
allow me to try accn of block w.r.t to ground = 30 5 /1 = 25 accn of plank w.r.t to ground = 30  5 /2 = 12.5 relative accn = 37.5 is that right?
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
idk...gime sm time i feel giddy
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
i still find something fishy in my solution.. hmm :
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
how do you say force on block 1 is 10 N? shouldnt the pseudo force be 30 N ?
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
as far as i kno pseudo is ma
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
well,,i'd argue there,,i maybe wrong,, anyways, that still doesnt yield the right ans, so got to be some flaw there..
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
ohh u from fiitjee?
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
am dropping my year for jee and ISI and CMI etc, living here in a remote place, just a small tuition like coaching here, no fitjee,resonance,akash here ,nearby i mean..
 one year ago

A.Avinash_GouthamBest ResponseYou've already chosen the best response.0
ohh i get it....it's okay......u have a better chance than any1 in here nd ur question....sry it's been long since i worked on these.........so i donno if i can help
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
hmmm ..nevermind,,thanks for trying sir! :)
 one year ago

sauravshakyaBest ResponseYou've already chosen the best response.0
dw:1356521627848:dw
 one year ago

sauravshakyaBest ResponseYou've already chosen the best response.0
So, accleration of the block with respect to the plank = 25/1 = 25ms^2
 one year ago

sauravshakyaBest ResponseYou've already chosen the best response.0
Now, s=ut+1/2 at^2 2=0+1/2 25 t^2 t^2=100 t=10seconds
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
@sauravshakya you missed out on the fact that the plank also moves, so the block wont have to cover 2m completely, if you get what i mean.
 one year ago

DiwakarBest ResponseYou've already chosen the best response.1
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 305=2a giving a=12.5m/s/s Eqn of motion for block is 1*a5=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**
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
thats where i went wrong, so it was a conceptual problem from my side..thanks a lot @Diwakar yep, thats the correct ans
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
just confirm me this, taking into account the pseudo force means A is the relative accn of block right ?
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
relative to the plank..
 one year ago

DiwakarBest ResponseYou've already chosen the best response.1
Yes, because we are working in the frame of the plank.
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
i understand this concept a lot better now..thanks..
 one year ago

DiwakarBest ResponseYou've already chosen the best response.1
acceleration w.r.t. ground can be found out as aA=12.57.5=5
 one year ago

DiwakarBest ResponseYou've already chosen the best response.1
.where a and A are the magnitudes. we used  sign because they point in opposite directions.
 one year ago

shubhamsrgBest ResponseYou've already chosen the best response.0
yep..again,,thanks a ton! :)
 one year ago
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