63. The wavelength associated with the unknown particle is λ
p
= h/p
p
= h/(m
p
v
p
), where p
p
is its momen-
tum, m
p
is its mass, and v
p
is its speed. The classical relationship p
p
= m
p
v
p
was used. Similarly, the
wavelength associated with the electron is λ
e
= h/(m
e
v
e
), where m
e
is its mass and v
e
is its speed. The
ratio of the wavelengths is λ
p
/λ
e
= (m
e
v
e
)/(m
p
v
p
), so
m
p
=
v
e
λ
e
v
p
λ
p
m
e
=
9.109
× 10
−31
kg
3(1.813
× 10
−4
)
= 1.675
× 10
−27
kg .
According to Appendix B, this is the mass of a neutron.