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A bomb at rest explodes into three parts of equal mass. If the momentum of two parts are \(-2 p \hat{\mathbf{i}}\) and \(p \hat{\mathbf{j}}\), find the magnitude of momentum of the third part.
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The correct answer is:
\(\sqrt{5} p\)
If \(p^{\prime} \hat{\mathbf{n}}\) be the momentum of third parts, then according to conservation of linear momentum. Total moment before explosion \(=\) Total momentum after explosion
\(\begin{array}{lll}
& \Rightarrow 0 =-2 p \hat{\mathbf{i}}+p \hat{\mathbf{j}}+p^{\prime} \hat{\mathbf{n}} \\
& \Rightarrow p^{\prime} \hat{\mathbf{n}} =2 p \hat{\mathbf{i}}-p \hat{\mathbf{j}} \\
& \therefore \text {Magnitude of } p^{\prime} \hat{\mathbf{n}}=p^{\prime} \\
& =\sqrt{(2 p)^2+(-p)^2}=\sqrt{5 p^2}=\sqrt{5 p}
\end{array}\)
\(\begin{array}{lll}
& \Rightarrow 0 =-2 p \hat{\mathbf{i}}+p \hat{\mathbf{j}}+p^{\prime} \hat{\mathbf{n}} \\
& \Rightarrow p^{\prime} \hat{\mathbf{n}} =2 p \hat{\mathbf{i}}-p \hat{\mathbf{j}} \\
& \therefore \text {Magnitude of } p^{\prime} \hat{\mathbf{n}}=p^{\prime} \\
& =\sqrt{(2 p)^2+(-p)^2}=\sqrt{5 p^2}=\sqrt{5 p}
\end{array}\)
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