Given:
- Initial speed (u) = 0 km/h (as the train starts from rest)
- Final speed (v) = 40 km/h
- Time (t) = 10 minutes = 10/60 = 1/6 hour

To find:
Acceleration (a)

Formula:
The formula to calculate acceleration is:
a = (v - u) / t

Calculation:
Substituting the given values into the formula:
a = (40 - 0) / (1/6)
a = 40 / (1/6)
a = 40 * 6/1
a = 240 km/h^2

Therefore, the acceleration of the train is 240 km/h^2.

Explanation:
To find the acceleration of the train, we can use the formula a = (v - u) / t, where v is the final velocity, u is the initial velocity, and t is the time taken.

In this case, the initial velocity (u) is given as 0 km/h because the train starts from rest. The final velocity (v) is given as 40 km/h. The time (t) is given as 10 minutes, which is converted to 1/6 hour.

Substituting these values into the formula, we get a = (40 - 0) / (1/6). Simplifying, we have a = 240 km/h^2.

Therefore, the acceleration of the train is 240 km/h^2.

Summary:
The train's acceleration is 240 km/h^2. The train starts from rest and reaches a speed of 40 km/h in 10 minutes. The formula used to calculate acceleration is a = (v - u) / t, where v is the final velocity, u is the initial velocity, and t is the time taken. By substituting the given values into the formula, we can calculate the acceleration.