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JIPMER 2007
Exam
JIPMER
Year
2007
Subject
Physics
Chapter
Mathematics in Physics

JIPMER 2007 · Physics · Mathematics in Physics

If the angle between the vectors A and B is θ , the value of the...

If the angle between the vectors A→\overrightarrow{\mathbf{A}} and B→\overrightarrow{\mathbf{B}} is θ\theta, the value of the product (B→×A→)⋅A→(\overrightarrow{\mathbf{B}} \times \overrightarrow{\mathbf{A}}) \cdot \overrightarrow{\mathbf{A}} is equal to

Options

  1. ABA2cos⁡θB A^2 \cos \theta
  2. BBA2sin⁡θB A^2 \sin \theta
  3. CBA2sin⁡θcos⁡θB A^2 \sin \theta \cos \theta
  4. Dzero

Correct answer

D. zero

Step-by-step solution

(B→×A→)⋅A→(\overrightarrow{\mathbf{B}} \times \overrightarrow{\mathbf{A}}) \cdot \overrightarrow{\mathbf{A}}=BAcos⁡θn→⋅A→=0\begin{aligned} & =B A \cos \theta \overrightarrow{\mathbf{n}} \cdot \overrightarrow{\mathbf{A}} \\ & =0\end{aligned}$HereHere\hat{\mathbf{n}}isperpendiculartobothis perpendicular to both\overrightarrow{\mathbf{A}} and \overrightarrow{\mathbf{B}}.Alternative:. Alternative :(\overrightarrow{\mathbf{B}} \times \overrightarrow{\mathbf{A}}) \cdot \overrightarrow{\mathbf{A}}Interchangethecrossanddot,wehave,Interchange the cross and dot, we have,(\overrightarrow{\mathbf{B}} \times \overrightarrow{\mathbf{A}}) \cdot \overrightarrow{\mathbf{A}}=\overrightarrow{\mathbf{B}} \cdot(\overrightarrow{\mathbf{A}} \times \overrightarrow{\mathbf{A}})=0 \quad(\because \overrightarrow{\mathbf{A}} \times \overrightarrow{\mathbf{A}}=0)NOTE:ThevolumeofaparallelopipedboundedbyvectorsNOTE: The volume of a parallelopiped bounded by vectors\overrightarrow{\mathbf{A}}, \overrightarrow{\mathbf{A}} and \overrightarrow{\mathbf{A}}canbeobtainedbygivingformulacan be obtained by giving formula(\overrightarrow{\mathbf{A}} \times \overrightarrow{\mathbf{A}}) \cdot \overrightarrow{\mathbf{A}}$
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