Given data: m = 10 kg; s = 20 m; g = 9.8 m/s² F = m.g = 10 × (-9.8) (The negative sign is taken because the displacement is opposite to the direction of the force.) F = -98 N W = F × s = -98 × 20 W = -1960 J (The negative sign appears because the direction of the force is opposite to the direction of displacement so that the work done is negative.)

Note: When work is done against gravity it is taken as negative and when gravity does work for us it is taken positively.

http://www.ncert.nic.in/ncerts/l/iesc111.pdf