Answer
The magnitude of the required force is $~~28.8~N$
Work Step by Step
To keep the car moving at a constant speed, an impulse is required which will give the added grain a momentum such that the grain's speed is equal to the car's speed.
We can find the magnitude of this impulse:
$J = m~\Delta v$
$J = (540~kg)~(3.20~m/s)$
$J = 1728~kg~m/s$
This impulse must be provided during each one-minute time period since 540 kg of grain are added each minute.
We can find the magnitude of the required force:
$F~t = J$
$F = \frac{J}{t}$
$F = \frac{1728~kg~m/s}{60~s}$
$F = 28.8~N$
The magnitude of the required force is $~~28.8~N$
