Practicing Success

Target Exam

CUET

Subject

-- Mathematics - Section B1

Chapter

Vectors

Question:

If \(\vec{a}\) and \(\vec{b}\)  are two collinear vectors, then which of the following are incorrect-

Options:

\(\vec{b}\)= λ\(\vec{a}\), for some scalar λ

\(\vec{a}\)= ±\(\vec{b}\)

the respective components of \(\vec{a}\)  and \(\vec{b}\) are proportional

both the components \(\vec{a}\) and \(\vec{b}\) have same direction, but different magnitude.

Correct Answer:

both the components \(\vec{a}\) and \(\vec{b}\) have same direction, but different magnitude.

Explanation:

If \(\vec{a}\)  and \(\vec{b}\)  are two collinear vectors, then they are parallel.

Therefore we have: \(\vec{b}\) = λ\(\vec{a}\), for some scalar λ = ±1 then \(\vec{a}\)= ±\(\vec{b}\)

If \(\vec{a}\)=  a1\(\hat{i}\) + a2\(\hat{j}\)+ a3\(\hat{j}\) and  \(\vec{b}\)=  b1\(\hat{i}\) + b2\(\hat{j}\)+ b3\(\hat{j}\) then

\(\vec{b}\) = λ\(\vec{a}\)

⇒  (b1\(\hat{i}\) + b2\(\hat{j}\)+ b3\(\hat{j}\))  = λ(a1\(\hat{i}\) + a2\(\hat{j}\)+ a3\(\hat{j}\))

⇒  (b1/a1) = (b2/a2) = (b3/a3) =λ

Thus  the respective components of \(\vec{a}\) and \(\vec{b}\)  are proportional.

However, vectors \(\vec{a}\) and \(\vec{b}\)   have different directions. Hence, the given statement in option (4) is incorrect.