Question

A uranium nucleus at rest decays into a thorium nucleus and a helium nucleus, as shown below. Which of the following is true?
${}_{92}^{235}U{\to }_{90}^{231}Th{+}_4^{2}He$

• 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

Answer: (D)

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

Apply the law of conservation of linear momentum,
$|P_{Th}|=|P_{He}|$
The kinetic energy of the element $K.E=\frac{P^2}{2m}$
m is the mass of the element
Hence,$K.E\propto \frac{1}{m}$
Kinetic energy is inversely proportional to the mass of element.
$m_{He}<m_{Th}$
$K.E_{He}>K.E_{Th}$
The helium nucleus has more kinetic energy than the thorium nucleus.