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A nucleus of uranium decays at rest into nuclei of thorium and helium. Then:

1. the helium nucleus has less momentum than the thorium nucleus.
2. the helium nucleus has more momentum than the thorium nucleus.
3. the helium nucleus has less kinetic energy than the thorium nucleus.
4. the helium nucleus has more kinetic energy than the thorium nucleus.

Correct answer: the helium nucleus has more kinetic energy than the thorium nucleus.

Solution

In nuclear decay, momentum is conserved. Since the helium nucleus is much lighter than the thorium nucleus, it must have a higher velocity to conserve momentum. Kinetic energy depends on both mass and velocity, and due to the helium nucleus's higher velocity, it will have more kinetic energy than the thorium nucleus.

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