IIT JEE , AIEEE Forum - Physics , Mechanics - NLM-friction #2

learner

In the figure,2kg block is pulled with constant force F.

What is the value of F so that tension btw blocks remains constant throughout during motion of blocks?

u=0.5

Ans:30N

Pl give explanation too..

Thanks!:-)

Salutes assured!!

ganesha1991

for the tension to be constant acceleration of the blocks must be zero
because if the blocks are accelerating then there acceleration for the 2 blocks will be different resulting in variation in tension
the equations for 2kg
F- T - 2

g = ma but a =0
therefore
F- T - 2

g=0
T = F - 2

g -------------------------------------------(1)

for 4kg
T - 4

g = ma
T - 4

g = 0
substituting value of T from (1)
F - 2

g - 4

g = 0
F = 6

g
    = 6 *0.5*10
    = 6*5
    = 30N

somyekathait

i have a doubt which i want to share with ganesha that how can the acceleration be zero even though a constant force is applied

ganesha1991

net force is zero .................................moves with constant velocity...i guess..........
but i didnt think about that ..............
but my approach to solving stated by me is right

dheer_07

he means acc is constant so that magnitude of force doesnt changes

learner

@Ganesha ...Thanks a lot for the detailed solution!!:-)

but could you please tell me the reason behind :

"for the tension to be constant acceleration of the blocks must be zero"

.

In the hint to this problem too it said the same..could you please tell me why?

I'm sorry,it may be a very basic doubt,but its not clear to me..

Thanks again!!!

deedee

force =ma

over here

tension=ma+u*mg

thus tension=m(a+ug)

u ,g,m r constant

thus a shud also b constant

m i rite??

ganesha1991

bro think both the blocks has acceleration...............
then there acceleration must be different as frictional force acting on them is different..........
so if the 1st block has more acceleration than the 2nd then tension between the blocks increases.........
now if the 1st block has less acceleration than the 2nd then the distance between the block decreases which results in decrease in tension...........................so if tension is to remain constant acceleration of the blocks must be 0

clear now

learner

Its clear now..thanks a lot!!!

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