IIT JEE , AIEEE Forum - Physics , Mechanics - if a body is in equilibrium under the action.....................

anil_kapoor

if a body is in equilibrium under the action of 3 copaner forces,then...
(a)-they must act i a straight line.
(b)-they must meet at a point
(c)-their horizontal and vertical components are equal
(d)-none of these....

Choose 1 correct answer, and plz give the appropriate reason to it.

rooney

1> Clearly Wrong.
2>This is true (In this case, rotational effect certainly wont be there. But there could be a case where the three forces dont pass through a point, still linear and rotational effects are zero)
3>NET Horizontal and vertical components should be zero. By what is given, one might infer that the horizontal and vertical components are equal BUT they could be of same sign too. But they need to be opposite in nature which is not given.

agnit_thebest

I think its (b)

anil_kapoor

answer is (a)

rooney

(a) is impossible.

anil_kapoor

tats given in the buk...

anil_kapoor

actually tats the Q if maths but totally bdependent on physics...
the buk is
R.D.SHARMA...
Pgno.52.2
Q-example-3

anil_kapoor

soln is .....
forces must meet in a pt or they must be parallel...

anil_kapoor

but i want more discription.

rooney

yaar its written "MUST act in a straight line " which is not ALWAYS true. So, (a) cant be the answer.

anil_kapoor

rooney

Suppose 2 forces pass through a given point. So, torque of these forces about this point is 0. Now, if third force DOES NOT pass thru this point, we will have some net resultant torque which will lead to non-equilibrium of the body through rotational motion. Hence, all 3 forces pass through a given point.

spideyunlimited

All three forces must meet at a point for the body to acheive equilibrium state, else some torque will be generated by the unbalanced force.
See, first consider any 2 forces out of the 3. Their resultant force will act in some direction, so the 3rd foce must oppose this force so will be opposite to their resultant force and meet them at the same point.

anil_kapoor

so tat simply means ......
if 2 of 3 forces are acting in some dir...so 3rd force must b acting in a st line of the resultant of those 2 frces....

i think this Q has multiple ans....buk says wrong ...a and b both seems 2 be correct.

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