Question

A particle acted on by constant forces $$4\hat i + \hat j - 3\hat k$$   and $$3\hat i + \hat j - \hat k$$   is displaced from the point $$\hat i + 2\hat j - 3\hat k$$   to the point $$5\hat i + 4\hat j + \hat k.$$    The total work done by the forces is :

A. $$50\,units$$
B. $$20\, units$$
C. $$30\, units$$
D. $$40\, units$$  
Answer :   $$40\, units$$
Solution :
$$\eqalign{ & \overrightarrow F + \overrightarrow {{F_1}} + \overrightarrow {{F_2}} = 7i + 2j - 4k \cr & \overrightarrow d = P.V.\,{\text{ of }}\overrightarrow B - P.V.{\text{ of }}\overrightarrow A = 4i + 2j - 2k \cr & W = \overrightarrow F .\overrightarrow d = 28 + 4 + 8 = 40{\text{ units}} \cr} $$

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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