A force →F=α^i+3^j+6^k is acting at a point →r=2^i−6^j−12^k. The value of α for which angular momentum about origin is conserved is:
A
-1
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B
2
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C
zero
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D
1
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Solution
The correct option is A -1 Here, →F=α^i+3^j+6^k
or, →F=Fx^i+Fy^j+Fz^k
and →r=2^i−6^j−12^k
or →r=x^i−y^j−z^k ∴Fxx=Fyy=Fzz
or, α2=3−6=6−12
or, −6α=6⇒α=−1