Question

What is j.j?

(a) 0

(b) 1

(c) -1

(d) ∞

This question was addressed to me in an interview for job.

My doubt is from Wedges topic in chapter Friction of Engineering Mechanics

Answer 1

Right choice is (b) 1

Explanation: As the dot product of only the same Cartesian component is unity, i.e. i.i = 1 and j.j =1, rest all remaining dot product will give 0(i.j = 0 and j.k = 0). Cross product of the same plane vectors always give zero. And dot product of the same plane vector gives a scalar quantity.