MCQ
A mass $m$ moving horizontally (along the $x-$ axis) with velocity $v$ collides and sticks to a mass of $3m$ moving vertically upward (along the $y-$ axis) with velocity $2v$. The final velocity of the combination is
  • A
    $\frac{3}{2}\,v\hat i + \frac{1}{4}\,v\hat j$
  • $\frac{1}{4}\,v\hat i + \frac{3}{2}\,v\hat j$
  • C
    $\frac{1}{3}\,v\hat i + \frac{2}{3}\,v\hat j$
  • D
    $\frac{2}{3}\,v\hat i + \frac{1}{3}\,v\hat j$

Answer

Correct option: B.
$\frac{1}{4}\,v\hat i + \frac{3}{2}\,v\hat j$
b
By conservation of linear momentum

$4 m \vec{v}_{c}=m v \hat{i}+3 m(2 v \hat{j}) \Rightarrow \vec{v}_{c}=\frac{v}{4} \hat{i}+\frac{3}{2} v \hat{j}$

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