Kinematics Question 301

Question: What is the value of linear velocity, if $ \vec{\omega }=3\hat{i}-4\hat{j}+\hat{k} $ and $ \vec{r}=5\hat{i}-6\hat{j}+6\hat{k} $ [CBSE PMT 1999; CPMT 1999, 2001; Pb. PMT 2000; Pb. CET 2000]

Options:

A) $ 2\hat{i}-4\hat{k} $

B) $ 4\hat{i}-8\hat{k} $

C) $ 2\hat{i}-4\hat{j}+2\hat{k} $

D) $ 4\hat{i}-8\hat{k} $

Show Answer

Answer:

Correct Answer: B

Solution:

Radius vector $ \vec{r}=\overrightarrow{r_2}-\overrightarrow{r_1}=(2\hat{i}-3\hat{j}+\hat{k})-(2\hat{i}+\hat{j}+\hat{k}) $ \ $ \vec{r}=-4\hat{j} $ Linear momentum $ \overrightarrow{p}=2\hat{i}+3\hat{j}-\hat{k} $

$ \vec{L}=\vec{r}\times \vec{p}=(-4\hat{j})\times (2\hat{i}+3\hat{j}-\hat{k}) $

$ = \begin{vmatrix} {\hat{i}} & {\hat{j}} & {\hat{k}} \\ 0 & -4 & 0 \\ 2 & 3 & -1 \\ \end{vmatrix} $

$ =4\hat{i}-8\hat{k} $



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