Laws Of Motion Question 429
Question: An explosion blows a rock into three parts. Two parts go off at right angles of each other. These two are 1 kg first part moving with a velocity of $ 12m{{s}^{-1}} $ and 2 kg second part moving with a velocity of$ 8m{{s}^{-1}} $ . If the third part files off with a velocity of $ 4m{{s}^{-1}}, $ its mass would be :
Options:
A) 5 kg
B) 7 kg
C) 17 kg
D) 3 kg
Show Answer
Answer:
Correct Answer: A
Solution:
[a] Apply law of conservation of linear momentum.
Momentum of first part $ =1\times 12=12kgm{{s}^{-1}} $ . Momentum of the second part $ =2\times 8=16kgm{{s}^{-1}} $ .
Resultant momentum $ =\sqrt{{{(12)}^{2}}+{{(16)}^{2}}}=20kgm{{s}^{-1}} $ .
The third part should also have the same momentum.
Let the mass of the third part be M, then $ 4\times M=20\Rightarrow M=5kg $
