MCQ
A projectile of mass $M$ is fired so that the horizontal range is $4\, km$. At the highest point the projectile explodes in two parts of masses $M/4$ and $3M/4$ respectively and the heavier part starts falling down vertically with zero initial speed. The horizontal range (distance from point of firing) of the lighter part is .................. $\mathrm{km}$
  • A
    $16$
  • B
    $1$
  • $10$
  • D
    $2$

Answer

Correct option: C.
$10$
c
$OQ=4\;km$

$QR=x\;km$

The centre of mass will hit the ground at point $Q$. As the haviour mass comes to rest after bracking

${x_{cm}} = \frac{{{m_1}{x_1} + {m_2}{x_2}}}{{{m_1} + {m_2}}}$

$\;Here\;{m_{1\;}} = \frac{{3M}}{4},{m_{2\;}} = \frac{M}{4},\;$$\;{x_{1\;}} = OP = 2,\;{x_{2\;}} = OR\; = \;4 + x$

So,

$4 = \frac{{\frac{{3M}}{4} \times 2 + \frac{M}{4} \times \left( {4 + x} \right)}}{M}$

$4M = \frac{{3M}}{2} + M\left( {1 + \frac{x}{4}} \right)1 + \frac{x}{4} $$= \frac{5}{2}\frac{x}{4} = \frac{3}{2}x = 6\;km$

Hence horizontal range of lighter particle is

$OR = OQ + QR = 4+6 = 10\; km$

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