Question

If $$\overrightarrow a .\overrightarrow i = \overrightarrow a .\left( {\overrightarrow i + \overrightarrow j } \right) = \overrightarrow a .\left( {\overrightarrow i + \overrightarrow j + \overrightarrow k } \right) = 1$$          then $$\overrightarrow a $$ is :

A. $$\overrightarrow i - \overrightarrow j $$
B. $$\overrightarrow i $$  
C. $$\overrightarrow j $$
D. $$\overrightarrow k $$
Answer :   $$\overrightarrow i $$
Solution :
$$\overrightarrow a .\overrightarrow i = 1,\,\overrightarrow a .\overrightarrow j = 0,\,\overrightarrow a .\overrightarrow k = 0.$$       These imply $$\overrightarrow a = \overrightarrow i $$

Releted MCQ Question on
Geometry >> 3D Geometry and Vectors

Releted Question 1

The scalar $$\vec A.\left( {\vec B + \vec C} \right) \times \left( {\vec A + \vec B + \vec C} \right)$$      equals :

A. $$0$$
B. $$\left[ {\vec A\,\vec B\,\vec C} \right] + \left[ {\vec B\,\vec C\,\vec A} \right]$$
C. $$\left[ {\vec A\,\vec B\,\vec C} \right]$$
D. None of these
Releted Question 2

For non-zero vectors $$\vec a,\,\vec b,\,\vec c,\,\left| {\left( {\vec a \times \vec b} \right).\vec c} \right| = \left| {\vec a} \right|\left| {\vec b} \right|\left| {\vec c} \right|$$       holds if and only if -

A. $$\vec a.\vec b = 0,\,\,\,\vec b.\vec c = 0$$
B. $$\vec b.\vec c = 0,\,\,\,\vec c.\vec a = 0$$
C. $$\vec c.\vec a = 0,\,\,\,\vec a.\vec b = 0$$
D. $$\vec a.\vec b = \vec b.\vec c = \vec c.\vec a = 0$$
Releted Question 3

The volume of the parallelepiped whose sides are given by $$\overrightarrow {OA} = 2i - 2j,\,\,\overrightarrow {OB} = i + j - k,\,\,\overrightarrow {OC} = 3i - k,$$         is :

A. $$\frac{4}{{13}}$$
B. $$4$$
C. $$\frac{2}{7}$$
D. none of these
Releted Question 4

The points with position vectors $$60i + 3j,\,\,40i - 8j,\,\,ai - 52j$$      are collinear if :

A. $$a = - 40$$
B. $$a = 40$$
C. $$a = 20$$
D. none of these

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