Question

An explosion blows a rock into three parts Two parts go off at right angles to each other. These two are, $1\, kg$ first part moving with a velocity of $12\, ms ^{-1}$ and $2\, kg$ second part moving with a velocity of $8\, ms ^{-1}$. If the thirds part files off with a velocity of $4\, ms ^{-1}$, its mass would be :

• A. 7 kg
• B. 17 kg
• C. 3 kg
• D. 5 kg

Answer 1

Answer: (D)

5 kg

Answer 2

$\vec{ P }_{1}+\vec{ P }_{2}+\vec{ P }_{3} =0$
$\mid \vec{ P }_{3} |=| \vec{ P }_{1}+\vec{ P }_{2} \mid$
$m \times 4 =\sqrt{ P _{1}^{2}+ P _{2}^{2}}$
$=\sqrt{12^{2}+16^{2}}$
$m =5\, kg$