A particle moves on a given straight line with a constant speed v. At a certain time it is at a point P on its straight line path. O is a fixed point. Show that →OP×→v is independent of the position P.
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Solution
Consider the particle moves on the straight line PP' at speed v.
OP x v = (OP) v sinФ n = v(OP) sinФ n = v(OQ) n
So,
OQ=OPsinФ=OP′sinФ
So, the magnitude of OPxv remain constant irrespective of the position of the particle.