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 $



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