Answer
1000 m/s
Work Step by Step
Assume that the neutron is not relativistic, and check the final answer to see if this make sense.
Relate the wavelength to the speed using equation 27–8.
$$\lambda=\frac{h}{p}=\frac{h}{mv}$$
$$v =\frac{h}{m \lambda }$$
$$v=\frac{6.63\times10^{-34}J \cdot s }{(1.67\times10^{-27}kg)(0.3\times10^{-9}m)}$$
$$=1323m/s\approx 1000 m/s$$
As we assumed, this is small compared to the speed of light, and the neutron is not relativistic.
