contestada

A neutron at rest decays (breaks up) to a proton and an electron. Energy is released in the decay and appears as kinetic energy of the proton and electron. The mass of a proton is 1836 times the mass of an electron. The mass of a proton is 1836 times the mass of an electron. What fraction of the total energy released goes into the kinetic energy of the proton?

Respuesta :

Answer:

[tex]5.44\times 10^-^4[/tex]

Explanation:

Let [tex]A[/tex] and [tex]B[/tex] represent proton and electron respectively

Total energy decay is:

[tex]Q=K_A+K_B[/tex] (1)

where [tex]K=\frac{1}{2} mv^2[/tex] (2)

The momentum of the particle is given by:

[tex]\overrightarrow{p}=m\overrightarrow{v}[/tex]

After the decay we have [tex]\overrightarrow{p}_A+ \overrightarrow{p}_B=0[/tex] (3)

Since the particles move in opposite direction,

[tex]\overrightarrow{p}_A=m_Av_A, \overrightarrow{p}_B=-m_Bv_B[/tex]

From eq (3) we get [tex]m_Av_A=m_Bv_B, v_B=v_A\frac{m_A}{m_B}[/tex] (4)

From eq (2) we get [tex]K_B=\frac{1}{2} mv_B^2[/tex]

From eq (1) and (4), [tex]Q=K_A+\frac{1}{2}m_B(v_A \frac{m_A}{m_B})^2[/tex]

[tex]Q=K_A+\frac{1}{2}m_Av_A^2 (\frac{m_A}{m_B})[/tex]

[tex]K_A=\frac{1}{2}m_Av_A^2,Q=K_A+K_A(\frac{m_A}{m_B})=K_A(1+\frac{m_A}{m_B})[/tex]

[tex]m_A=1836m_B ,Q=K_A(1+1836)[/tex]

[tex]\frac{K_A}{Q}=\frac{1}{1837}=5.44\times 10^-^4[/tex]