IIT JEE , AIEEE Forum - Physics , Mechanics

varun.tinkle

A SMALL HEAVY BOCK IS ATTATCHED TO A LIGHT ROD OF LENGTH l WHICH CAN BE ROTATED ABUOT ITS CLAMPED UPPER END.WHAT MINIMUM HORIZONTAL VELOCITY SHOULD BE GIVEN SO THAT IT MOVES IN A COMPLETE CIRCLE

ANS UNDER ROOT 4GL

MY STEP IS THAT THE BLOCK MOVES IN A CIRCLE OF RADIUS l SO AT THE TOPMOST POINT MV^2/L=MG

V^2=LG

THE POTENTIAL ENERGY IS 2MGL

SO

1/2MV1^2=1/2MV^2+MGH

SOLVING IT WE GET V

AS UNDER ROOT 5LG

BUT THE ANSWER IS WRONG

PLS EXPLN THE FLAW IN MY WORKING

sboosy

The important point is that it is a rod and not a string ..a string can slack but a rod cannot

Thus the least condition is that the topmost pt ..the velocity can be 0 .

thus mg(2l) = 1/2 m(v²)

which means v =

4gl

Decoder

at topmost pt.. velocity of rod is zero..so no instataneous centripetal acc..

in string the tension becomes zero..but in case of rod..it is actually negative..

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