Question

An explosion breaks a rock into three parts in a horizontal plane. Two of them go off at right angles to each other. The first part of mass $1\, kg$ moves with a speed of $12 \, ms^{-1}$ and the second part of mass $2 \,kg$ moves with $8 \, ms^{-1}$ speed. If the third part files off with $4 \, ms^{-1}$ speed, then its mass is :

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

Answer 1

Answer: (C)

5 kg

Answer 2

From conservation of momentum
$m(4) = \sqrt{ (1 \times 12)^2 + (2 \times 8)^2} \Rightarrow m = 5 kg$