Question

Pls I need help I would mark you as the brainliest answer! A train starting from rest attains a velocity 72 km / h in 5 minutes. Assuming that the acceleration is uniform, find the acceleration.

Answer 1

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.

(14.4km/hr·minute)·(1000m/km)·(1 hour/60minutes)·(1 minute/60seconds)²

= (14.4·1000 / 60·60·60) · (km·meter·hr·min·min / hr·min·km·min·sec·sec) 

= 0.0667 meter/second²

With similar methods, it could be changed to other units:

-- 6.67 centimeter/second²
-- 66.7 millimeter/second²
-- 240 meter/minute²
-- 864 km/hour²

These are all THE SAME NUMBER, only with different units.