SATHEE: Kinematics Question 296

Kinematics Question 296

Question: The value of $(\vec{A} + \vec{B}) \times (\vec{A} - \vec{B})$ it’s [RPET 1991, 2002; BHU 2002]

Options:

A) $14 \hat{i} - 38 \hat{j} + 16 \hat{k}$

B) $4 \hat{i} + 4 \hat{j} + 6 \hat{k}$

C) $21 \hat{i} + 4 \hat{j} + 4 \hat{k}$

D) $- 14 \hat{i} + 34 \hat{j} - 16 \hat{k}$

Show Answer

Answer:

Correct Answer: A

Solution:

$\vec{τ} = \vec{r} \times \vec{F} = (7 \hat{i} + 3 \hat{j} + \hat{k}) (- 3 \hat{i} + \hat{j} + 5 \hat{k})$

$\vec{τ} = | \begin{matrix} \hat{i} & \hat{j} & \hat{k} \\ 7 & 3 & 1 \\ - 3 & 1 & 5 \end{matrix} |$

$= 14 \hat{i} - 38 \hat{j} + 16 \hat{k}$

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Kinematics Question 296

Question: The value of (A→+B→)×(A→−B→) it’s [RPET 1991, 2002; BHU 2002]

Options:

Answer:

Solution:

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Question: The value of $(\vec{A} + \vec{B}) \times (\vec{A} - \vec{B})$ it’s [RPET 1991, 2002; BHU 2002]