How will the weight of an 20kg object change if it was in a lift that accelerates downwards at 4m.s-1

Answer 1

The weight as measured on a scale would be reduced by M*a,
from M*g to M*(g-a)
where a is the downward acceleration.
That is a reduction of 4/9.8 = 40.8%

If the scale is calibrated in kg, it would read 14.8 kg. They may want you to convert that to Newtons.

Answer 2

When an object is moving downwards its weight is 0kg.Because is in free-fall experiences the gravitational force.