We are given that the train passes a telegraph post in 40 seconds and moves at a rate of 36 km/h. First, we convert the speed to meters per second:
\[
\text{Speed} = 36 \, \text{km/h} = \frac{36 \times 1000}{3600} = 10 \, \text{m/s}
\]
The distance traveled by the train in 40 seconds is:
\[
\text{Distance} = \text{Speed} \times \text{Time} = 10 \, \text{m/s} \times 40 \, \text{s} = 400 \, \text{m}
\]
Thus, the length of the train is 400 meters.