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If \left | A \right |=2 and \left | B \right |=4 then match the relations in column I with the angle \theta between A and B in column II.

    Column I                          Column II

(a)\left | A\times B \right |=0          (i) \theta =30^{o}

(b) \left | A\times B \right |=8         (ii) \theta =45^{o}

(c) \left | A\times B \right |=4         (iii) \theta =90^{o}

(d) \left | A\times B \right |=4\sqrt{2}    (iv) \theta =0^{o}

 

Answers (1)

Given : \left | \vec{A} \right |=2 and \left | \vec{B} \right |=4

a) Matches with (iv)

\left | \vec{A}\times \vec{B} \right |=0

\left | \vec{A} \right |\left | \vec{B} \right |\sin \theta =0

2\times4\; \sin \theta =0

\sin \theta =\sin 0

\theta =0

b) matches with (iii)

\left | \vec{A}\times \vec{B} \right |=8

\left | \vec{A} \right |\left | \vec{B} \right |\sin \theta =8

2\times4\; \sin \theta =8

\sin \theta =1

\theta =90

c) matches with (i)

\left | \vec{A}\times \vec{B} \right |=4

\left | \vec{A} \right |\left | \vec{B} \right |\sin \theta =4

2\times4\; \sin \theta =4

\sin \theta =\frac{1}{2}

\theta =30

d) matches with (ii)

\left | \vec{A}\times \vec{B} \right |=4\sqrt{2}

\left | \vec{A} \right |\left | \vec{B} \right |\sin \theta =4\sqrt{2}

2\times4\; \sin \theta =4\sqrt{2}

\sin \theta =\frac{1}{\sqrt{2}}

\theta =45

 

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