Question
A radioactive nucleus of mass number 'A', initially at rest, emits an α - particle with a speed 'v'. What will be the recoil speed of the daughter nucleus?
Answer: Option C
:
C
The total number of nucleons (i.e. protons + neutrons) in a nucleus is called its mass number. An α-particleis a helium nucleus having 2 protons and 2 neutrons. So the mass number of an α - particle = 4. When anucleus of mass number A emits an α - particle, the mass number of the daughter nucleus reduces to(A – 4). If V is the recoil speed of the daughter nucleus, we have, from the law of conservation ofmomentum, (A – 4)V-4v = 0
or V=4vA−4
Hence the correct choice is (c)
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:
C
The total number of nucleons (i.e. protons + neutrons) in a nucleus is called its mass number. An α-particleis a helium nucleus having 2 protons and 2 neutrons. So the mass number of an α - particle = 4. When anucleus of mass number A emits an α - particle, the mass number of the daughter nucleus reduces to(A – 4). If V is the recoil speed of the daughter nucleus, we have, from the law of conservation ofmomentum, (A – 4)V-4v = 0
or V=4vA−4
Hence the correct choice is (c)
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