Aconveyor belt at a quarry lifts 1,800 kg of sand per minute up a vertical distance of 9.5 meters. the sand is initially at rest, then moves at a speed of 0.28 m/s along the conveyor belt. what is the instantaneous power generated by this machine?

I think you have more numbers in the question than are necessary.
Let's see.

To  raise 1,800 kg to a height of 9.5 meters,
you have to give it

         (mass) x (gravity) x (height)              of potential energy

  =    (1,800 kg) x (9.8 m/s²) x (9.5 m)

  =         167,580 joules of energy .

Power = (work done) / (time to do the work)

           =  (167,580 joules / 1 minute) x (1 minute / 60 seconds)

           =  2,793 joules/second  =  2,793 watts AVERAGE.

I'm not sure why the 0.28 m/s needs to be there.  Maybe it wants us
to add the kinetic energy of the moving sand, but that's a bogus detail. 
The average power to get the sand up to the top of the 9.5 meters in
1 minute is 2,793 watts.  If some of it goes to give the sand some kinetic
energy along the way, then towards the end, the kinetic energy will turn
into potential energy anyway, as the sand 'coasts' to the top and comes
to rest, and that'll be a little less power that the machine has to supply
during the last few seconds.  So the instantaneous power varies along
the way ... more at the beginning to accelerate the sand, less at the end
when the sand coasts to a stop ... and I don't think we can be any more
precise than to calculate the average for the minute.

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