BoardMaths

Vector Algebra

31 Board Maths previous year questions on Vector Algebra — options free on every question; 3 include the answer & explanation free, the rest unlock with PYQ Pass.

Q1 FREE PREVIEW
PYQ

\(\text{ If }\vec{a}\text{ and }\vec{b}\text{ are two unit vectors, then }\vec{a}\cdot \vec{b}=...........\)

a

\(\cos \left(\theta \right)\)

b

\(\sin \left(\theta \right)\)

c

\(ab\cos \left(\theta \right)\)

d

\(ab\sin \left(\theta \right)\)

✓ Correct answer: a)

\(\cos \left(\theta \right)\)

Explanation

|a|=1 , |b|=1 because they are the unit vectors.

Q2 FREE PREVIEW
PYQ

\((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\)

a

\(9\vec{i}-\vec{j}+3\vec{k}\)

b

\(9\vec{i}+\vec{j}-3\vec{k}\)

c

\(\vec{i}-\vec{j}+3\vec{k}\)

d

\(\vec{i}+\vec{j}-3\vec{k}\)

✓ Correct answer: a)

\(9\vec{i}-\vec{j}+3\vec{k}\)

Explanation

The given vectors are \((\vec{i}+3\vec{j}-2\vec{k})\) and \((-\vec{i}+3\vec{k})\).

\((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})\) represents the cross product of two vectors.

\((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\left|\begin{matrix}\vec{i} & \vec{j} & \vec{k} \\ 1 & 3 & -2 \\ -1 & 0 & 3\end{matrix}\right|\\ (\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\vec{i}\left|\begin{matrix}3 & -2 \\ 0 & 3\end{matrix}\right|-\vec{j}\left|\begin{matrix}1 & -2 \\ -1 & 3\end{matrix}\right|+\vec{k}\left|\begin{matrix}1 & 3 \\ -1 & 0\end{matrix}\right|\\ (\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\vec{i}(9-0)-\vec{j}(3-2)+\vec{k}(0+3)\\ (\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=9\vec{i}-\vec{j}+3\vec{k}\)

Hence, the value of \((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})\) is \(9\vec{i}-\vec{j}+3\vec{k}.\)

Q3 FREE PREVIEW
PYQ

Let \(\vec{p}\) and \(\vec{q}\) be two unit vectors and \(\alpha\) be the angle between them. Then \((\vec{p}+\vec{q})\) will be a unit vector for what value of \(\alpha\) ?

a

\(\frac{\pi }{4}\)

b

\(\frac{\pi }{3}\)

c

\(\frac{\pi }{2}\)

d

\(\frac{2\pi }{3}\)

✓ Correct answer: d)

\(\frac{2\pi }{3}\)

Explanation

Given, \(\left|\vec{p}+\vec{q}\right|=\left|\vec{p}\right|=\left|\vec{q}\right|=1\)

Now,

\({\left|\vec{p}+\vec{q}\right|}^{2}={\left|\vec{p}\right|}^{2}+{\left|\vec{q}\right|}^{2}+2\vec{p}\cdot \vec{q}\)

\(\Rightarrow {1}^{2}=1+1+2\cos \alpha\)

\(\Rightarrow 1=2+2\cos \alpha\)

\(\Rightarrow \cos \alpha =-\frac{1}{2}\)

\(\Rightarrow \alpha =\frac{2\pi }{3}\)

Q4
PYQ

\(\text{ If }\vec{a}\text{ and }\vec{b}\text{ are two unit vectors, then }\vec{a}\cdot \vec{b}=...........\)

a

\(\cos \left(\theta \right)\)

b

\(\sin \left(\theta \right)\)

c

\(ab\cos \left(\theta \right)\)

d

\(ab\sin \left(\theta \right)\)

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Q5
PYQ

Let \(\vec{a}=2\hat{i}−\hat{j}+\hat{k}\) and \(\vec{b}=\lambda \hat{j}+2\hat{k},\text{  }\lambda \in Z\) be the two vectors. Let \(\vec{c}=\vec{a}\times \vec{b}\) and \(\vec{d}\) be the vector of magnitude \(2\) in \(yz\)-plane. If \(\left|\vec{c}\right|=\sqrt{53},\) then the maximum possible value of \((\vec{c} \cdot \vec{d})^2\) is equal to:

[JEE Main 2026, 22 Jan (Shift 2)]

a

208

b

26

c

104

d

52

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Q6
PYQ

\(\left|\vec{i}-\vec{j}-\vec{k}\right|=\)

a

\(\sqrt{3}\)

b

\(3\)

c

\(\sqrt{2}\)

d

\(2\)

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Q7
PYQ

For any two vectors \(\vec{a}\) and \(\vec{b}\), which of the following statements is always true?

a

\(\vec{a} \cdot \vec{b} \geq|\vec{a}||\vec{b}|\)

b

\(\quad \vec{a} \cdot \vec{b}=|\vec{a}||\vec{b}|\)

c

\(\overrightarrow{\mathrm{a}} \cdot \overrightarrow{\mathrm{b}} \leq|\overrightarrow{\mathrm{a}}||\overrightarrow{\mathrm{b}}|\)

d

\(\quad \vec{a} \cdot \vec{b}<|\vec{a}||\vec{b}|\)

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Q8
PYQ

For any two vectors \(\vec{a}\) and \(\vec{b}\), which of the following statements is always true?

a

\(\vec{a} \cdot \vec{b} \geq|\vec{a}||\vec{b}|\)

b

\(\quad \vec{a} \cdot \vec{b}=|\vec{a}||\vec{b}|\)

c

\(\overrightarrow{\mathrm{a}} \cdot \overrightarrow{\mathrm{b}} \leq|\overrightarrow{\mathrm{a}}||\overrightarrow{\mathrm{b}}|\)

d

\(\quad \vec{a} \cdot \vec{b}<|\vec{a}||\vec{b}|\)

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Q9
PYQ

The projection vector of vector \(\vec{a}\) on vector \(\vec{b}\) is

a

\(\left(\frac{\vec{a}\cdot \vec{b}}{|\vec{b}{|}^{2}}\right)\vec{b}\)

b

\(\frac{\vec{a}\cdot \vec{b}}{|\vec{b}|}\)

c

\(\frac{\vec{a}\cdot \vec{b}}{|\vec{a}|}\)

d

\(\left(\frac{\vec{a}\cdot \vec{b}}{|\vec{a}{|}^{2}}\right)\vec{b}\)

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Q10
PYQ

The vector with terminal point \(\mathrm{A}(2,-3,5)\) and initial point \(\mathrm{B}(3,-4,7)\) is :

a

\(\hat{i}-\hat{j}+2 \hat{k}\)

b

\(\hat{i}+\hat{j}+2 \hat{k}\)

c

\(-\hat{i}-\hat{j}-2 \hat{k}\)

d

\(-\hat{i}+\hat{j}-2 \hat{k}\)

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Q11
PYQ

The unit vector perpendicular to both vectors \(\hat{i}+\hat{k}\) and \(\hat{i}-\hat{k}\) is:

a

\(2 \hat{j}\)

b

\(\hat{j}\)

c

\(\frac{\hat{\mathrm{i}}-\hat{\mathrm{k}}}{\sqrt{2}}\)

d

\(\frac{\hat{\mathrm{i}}+\hat{\mathrm{k}}}{\sqrt{2}}\)

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Q12
PYQ

The projection vector of \(\vec{a}\) on \(\vec{b}\) is

a

\(\left(\frac{\vec{a}\cdot \vec{b}}{|\vec{b}{|}^{2}}\right)\vec{b}\)

b

\(\frac{\vec{a}\cdot \vec{b}}{|\vec{b}|}\)

c

\(\frac{\vec{a}\cdot \vec{b}}{|\vec{a}|}\)

d

\(\left(\frac{\vec{a}\cdot \vec{b}}{|\vec{a}{|}^{2}}\right)\vec{b}\)

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Q13
PYQ

\(\vec{j}.\vec{j}=\)

a

\(0\)

b

\(1\)

c

\(-1\)

d

\(\vec{k}\)

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Q14
PYQ

\((4\vec{i}+3\vec{j}+3\vec{k}).(6\vec{i}-4\vec{j}+\vec{k})=\)

a

\(22\)

b

\(15\)

c

\(21\)

d

\(18\)

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Q15
PYQ

The position vectors of points P and Q are \(\vec{p}\) and \(\vec{q}\) respectively. The point R divides line segment PQ in the ratio 3: 1 and S is the mid-point of line segment PR. The position vector of S is :

a

\(\frac{\vec{\mathrm{p}}+3\vec{\mathrm{q}}}{4}\)

b

\(\frac{\vec{\mathrm{p}}+3\vec{\mathrm{q}}}{8}\)

c

\(\frac{5\vec{p}+3\vec{q}}{4}\)

d

\(\frac{5\vec{\mathrm{p}}+3\vec{\mathrm{q}}}{8}\)

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Q16
PYQ

\((\vec{i}+3\vec{j}-2\vec{k})\times (-\vec{i}+3\vec{k})=\)

a

\(9\vec{i}-\vec{j}+3\vec{k}\)

b

\(9\vec{i}+\vec{j}-3\vec{k}\)

c

\(\vec{i}-\vec{j}+3\vec{k}\)

d

\(\vec{i}+\vec{j}-3\vec{k}\)

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Q17
PYQ

Let \(\theta\) be the angle between two unit vectors \(\hat{\mathrm{a}}\) and \(\hat{\mathrm{b}} \operatorname{such}\) that \(\sin \theta=\frac{3}{5}\). Then, \(\hat{a} \cdot \hat{b}\) is equal to :

a

\(\pm \frac{3}{5}\)

b

\(\pm \frac{3}{4}\)

c

\(\pm \frac{4}{5}\)

d

\(\pm \frac{4}{3}\)

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Q18
PYQ

Let \(\theta\) be the angle between two unit vectors \(\hat{\mathrm{a}}\) and \(\hat{\mathrm{b}} \operatorname{such}\) that \(\sin \theta=\frac{3}{5}\). Then, \(\hat{a} \cdot \hat{b}\) is equal to :

a

\(\pm \frac{3}{5}\)

b

\(\pm \frac{3}{4}\)

c

\(\pm \frac{4}{5}\)

d

\(\pm \frac{4}{3}\)

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Q19
PYQ

The unit vector perpendicular to both vectors \(\hat{i}+\hat{k}\) and \(\hat{i}-\hat{k}\) is:

a

\(2 \hat{j}\)

b

\(\hat{j}\)

c

\(\frac{\hat{\mathrm{i}}-\hat{\mathrm{k}}}{\sqrt{2}}\)

d

\(\frac{\hat{\mathrm{i}}+\hat{\mathrm{k}}}{\sqrt{2}}\)

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Q20
PYQ

The vector with terminal point \(\mathrm{A}(2,-3,5)\) and initial point \(\mathrm{B}(3,-4,7)\) is :

a

\(\hat{i}-\hat{j}+2 \hat{k}\)

b

\(\hat{i}+\hat{j}+2 \hat{k}\)

c

\(-\hat{i}-\hat{j}-2 \hat{k}\)

d

\(-\hat{i}+\hat{j}-2 \hat{k}\)

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Q21
PYQ

\((4\vec{i}+3\vec{j}+3\vec{k}).(6\vec{i}-4\vec{j}+\vec{k})=\)

a

\(22\)

b

\(15\)

c

\(21\)

d

\(18\)

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Q22
PYQ

\(\vec{j}.\vec{j}=\)

a

\(0\)

b

\(1\)

c

\(-1\)

d

\(\vec{k}\)

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Q23
PYQ

Let \(\vec{p}\) and \(\vec{q}\) be two unit vectors and \(\alpha\) be the angle between them. Then \((\vec{p}+\vec{q})\) will be a unit vector for what value of \(\alpha\) ?

a

\(\frac{\pi }{4}\)

b

\(\frac{\pi }{3}\)

c

\(\frac{\pi }{2}\)

d

\(\frac{2\pi }{3}\)

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Q24
PYQ

The position vectors of points \(P\) and \(Q\) are \(\vec{p}\) and \(\vec{q}\) respectively. The point \(R\) divides line segment \(PQ\) in the ratio \(3:1\) and \(S\) is the mid-point of line segment \(PR\). The position vector of \(S\) is :

a

\(\frac{\vec{\mathrm{p}}+3\vec{\mathrm{q}}}{4}\)

b

\(\frac{\vec{\mathrm{p}}+3\vec{\mathrm{q}}}{8}\)

c

\(\frac{5\vec{p}+3\vec{q}}{4}\)

d

\(\frac{5\vec{\mathrm{p}}+3\vec{\mathrm{q}}}{8}\)

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Q25
PYQ

\(\left|\vec{i}-\vec{j}-\vec{k}\right|=\)

a

\(\sqrt{3}\)

b

\(3\)

c

\(\sqrt{2}\)

d

\(2\)

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Q26
PYQ

If \(\vec{a}\) and \(\vec{b}\) are two non-zero vectors, then \(\vec{a}\cdot \vec{b}=-|\vec{a}||\vec{b}|\), if -

a

\(\theta =\frac{\pi }{2}\)

b

\(\theta =0^\circ\)

c

\(\theta =\pi\)

d

\(\theta =\frac{3\pi }{2}\)

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Q27
PYQ

\(1+{\cot }^{2}\theta =\)

a

\({\sin }^{2}\theta\)

b

\({\csc }^{2}\theta\)

c

\({\tan }^{2}\theta\)

d

\({\sec }^{2}\theta\)

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Q28
PYQ

If the magnitude of two vectors \(\vec{a}\) and \(\vec{b}\) are \(\sqrt{3}\) and 2 respectively and \(\vec{a}\cdot \vec{b}=\sqrt{6}\), then the angle between \(\vec{a}\) and \(\vec{b}\) is -

a

\(\frac{\pi }{2}\)

b

\(\frac{\pi }{3}\)

c

\(\frac{\pi }{6}\)

d

\(\frac{\pi }{4}\)

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Q29
PYQ

The value of \(\hat{i}\cdot (\hat{j}\times \hat{k})+\hat{j}\cdot (\hat{i}\times \hat{k})+\hat{k}\cdot (\hat{i}\times \hat{j})\) is -

a

0

b

-1

c

1

d

3

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Q30
PYQ

The value of \(\hat{i}\cdot (\hat{j}\times \hat{k})+\hat{j}\cdot (\hat{i}\times \hat{k})+\hat{k}\cdot (\hat{i}\times \hat{j})\) is:

a

0

b

-1

c

1

d

3

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Q31
PYQ

Direction : Two statements are given one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the following options :
Assertion (A) : The vectors

\(\vec{\mathrm{a}}=6\hat{\mathrm{i}}+2\hat{\mathrm{j}}-8\hat{\mathrm{k}}\\ \vec{\mathrm{b}}=10\hat{\mathrm{i}}-2\hat{\mathrm{j}}-6\hat{\mathrm{k}}\\ \vec{\mathrm{c}}=4\hat{\mathrm{i}}-4\hat{\mathrm{j}}+2\hat{\mathrm{k}}\)

represent the sides of a right angled triangle.
Reason (R) : Three non-zero vectors of which none of two are collinear forms a triangle if their resultant is zero vector or sum of any two vectors is equal to the third.

a

Both Assertion (A) and Reason (R) are true and the Reason (R) is the correct explanation of the Assertion (A).

b

Both Assertion (A) and Reason (R) are true and Reason (R) is not the correct explanation of the Assertion (A).

c

Assertion (A) is true, but Reason (R) is false.

d

Assertion (A) is false, but Reason (R) is true.

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