Question

$$ABCDEF$$    is a regular hexagon where centre $$O$$ is the origin. If the position vectors of $$A$$ and $$B$$ are $$\hat i - \hat j + 2\hat k$$   and $$2\hat i + \hat j - \hat k$$   respectively then $$\overrightarrow {BC} $$  is equal to :

A. $$\hat i + \hat j - 2\hat k$$
B. $$ - \hat i + \hat j - 2\hat k$$  
C. $$3\hat i + 3\hat j - 4\hat k$$
D. none of these
Answer :   $$ - \hat i + \hat j - 2\hat k$$
Solution :
$$\eqalign{ & \overrightarrow {OA} = \hat i - \hat j + 2\hat k,\,\,\overrightarrow {OB} = 2\hat i + \hat j - \hat k \cr & \therefore \,\overrightarrow {OC} = \overrightarrow {AB} = \overrightarrow {OB} - \overrightarrow {OA} \cr & = \hat i + 2\hat j - 3\hat k \cr} $$
3D Geometry and Vectors mcq solution image
$$\eqalign{ & \therefore \,\overrightarrow {BC} = \overrightarrow {OC} - \overrightarrow {OB} \cr & = \left( {\hat i + 2\hat j - 3\hat k} \right) - \left( {2\hat i + \hat j - \hat k} \right) \cr & = - \hat i + \hat j - 2\hat k \cr} $$

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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