Question

A uranium nucleus at rest decays into a thorium nucleus and a helium nucleus, as shown below. Which of the following is true?

${}_{92}^{235}U{\to }_{90}^{231}Th{+}_2^{4}He$

• A. Each decay product has the same kinetic energy.
• B. The decay products tend to go in the same direction.
• C. The thorium nucleus has more momentum than the helium nucleus.
• D. The helium nucleus has more kinetic energy than the thorium nucleus.

Answer 1

The correct option is D

The helium nucleus has more kinetic energy than the thorium nucleus.

Law of conservation of momentum is applicable.

$\therefore (MV{)}_{Th}=-(mv{)}_{He}\Rightarrow |(MV{)}_{Th}|=|(mv{)}_{He}|=p\left(say\right)\therefore (KE{)}_{Th}=\frac{p^2}{2M}and(KE{)}_{He}=\frac{p^2}{2m}Obviously,(KE{)}_{Th}<(KE{)}_{He}(\because M>m)$