Here's all the Physics you have to know in order to answer this question:
==> Acceleration = (change in speed) / (time for the change)
That's it. Now let's work on it with the numbers from the train.
Change in speed = (speed at the end) - (speed at the beginning)
For the train, speed at the beginning is zero, so the change is 72 km/h .
Time for the change = 5 minutes.
Acceleration = (72 km/hr) / (5 minutes)
Acceleration = 14.4 km per hour per minute .
That answer is 100% true and correct, but it has a weird, awkward unit. Anybody you show it to would probably want to see it with a more familiar unit, like "meters per second per second" like the unit that we use for the acceleration of gravity. It's pretty easy to change units, and it doesn't even take any Physics. All it takes is Arithmetic.
So far, we have Acceleration = 14.4 km/hr·minute
Multiply that by (1000 meter/km) Then multiply it by (1 hour/60 minutes). Then multiply it by (1 minute/60 seconds)². All of these fractions are equal to ' 1 ', because each top number is equal to each bottom number. So they won't change the VALUE of the answer. They'll just change the units.
The inner membrane has many overlapping folds called cristae. Inside the inner membrane there is the mitochondrial matrix, it contains enzymes that are used in creating ATP. You're welcome. :)