A stationary nucleus has nucleon number A. The nucleus decays by emitting a proton with speed "v" to form a new nucleus with speed u. The new nucleus and the proton move away from one another in opposite directions. Which equation gives "v" in terms of A and u?
Correct answer: B. v=(A-1)u
- A. v=(A/4-1)u
- B. v=(A-1)u
- C. v=Au
- D. v=(A+1)u
Explanation
D P=v, N=u, AAccording to the law of conservation of momentum, P(initial)= P(final)Pi is zero because system is at rest but Pf is equal to the sum of momentum of nucleus and momentum of proton.If 1 proton is emitted then the atomic number is reduced by 1. Therefore,0=MnVn+MpVp0 =(A-1)u +1vPutting negative sign with v because the direction is opposite 0=(A-1)u -1V1V= (A-1)u
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