Kinematics Question 580

Question: If the resultant of the vectors $ 3\widehat{i}+4\widehat{j}+5\widehat{k} $ and $ 5\widehat{i}+3\widehat{j}+4\widehat{k} $ makes an angle $ \theta $ with x-axis, then $ cos90{}^\circ $ it’s

Options:

A) 0.07

B)0.574

C) 0.111

D)0.123

Show Answer

Answer:

Correct Answer: B

Solution:

[b] The resultant vector$ =( 3\hat{i}+4\hat{j}+5\hat{k} )+( 5\hat{i}+3\hat{j}+4\hat{k} )=8\hat{i}+7\hat{j}+9\hat{k} $

$ \cos \theta =\frac{8}{\sqrt{8^{2}+7^{2}+9^{2}}}=0.574 $



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