1. **Problem Statement:** A train travels at 40 m/s and takes 2.0 s to pass a man standing by the railway track. Find the length of the train. 2. **Formula Used:** The length of the train can be found using the formula for distance: $$\text{Distance} = \text{Speed} \times \text{Time}$$ 3. **Explanation:** Here, the distance the train covers while passing the man is equal to the length of the train because the entire train passes the man in the given time. 4. **Calculation:** $$\text{Length of train} = 40 \text{ m/s} \times 2.0 \text{ s} = 80 \text{ m}$$ 5. **Answer:** The length of the train is 80 meters. Therefore, the correct option is D 80 m.