A force →F = αî + 3ĵ + 6̂k is

A force ^→F = αî + 3ĵ + 6̂k is acting at a point ^→r = 2î - 6ĵ - 12̂k . The value of α for which angular momentum about origin is conserved is :

From Newton's second law for rotational motion,

(2î - 6ĵ - 12&770;k) × (αî + 3ĵ + 6̂k) = 0
Solving we get α = –1