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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 m/s and 2 kg second part moving with a velocity of 8 m/s. If the third part flies off with a velocity of 4 m/s, its mass would be

A
5 kg
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B
7 kg
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C
3 kg
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D
17 kg
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Solution

The correct option is A 5 kg
Draw a diagram of given situation.

Find the mass of third part.
Formula used: p=mv
Given,
m1=1 kg
v1=12 m/sec
m2=2 kg
v2=8 m/sec
m3=m
v3=4 m/sec
Momentum of first part,
p1=m1v1=1×12=12 kg m/sec
Momentum of second part,
p2=m2v2=2×8=16 kg m/sec
Resultant momentum of two parts is,
(1×12)2+(2×8)2=20 kg m/sec
p3=m3v3=20 kg m/sec
Momentum of third part,
20=m×4 m=5 kg
Final Answer: (A)


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