Answer
$F = 46~N$
Work Step by Step
We can express $10~km/h$ in units of $m/s$:
$(10~km/h)(\frac{1~h}{3600~s})(\frac{1000~m}{1~km}) = 2.78~m/s$
We can express $20~km/h$ in units of $m/s$:
$(20~km/h)(\frac{1~h}{3600~s})(\frac{1000~m}{1~km}) = 5.56~m/s$
In order to maintain the same speed, the coal needs to be accelerated from $10~km/h$ to $20~km/h$ in one minute.
We can find the required acceleration:
$a = \frac{5.56~m/s-2.78~m/s}{60~s} = 0.0463~m/s^2$
We can find the required force:
$F = ma$
$F = (1000~kg)(0.0463~m/s^2)$
$F = 46~N$
