The General Question
Which of the following is grammatically correct?
It's not good for him or her.
It's not good for him and her.
either...or structure is a very safe alternative:
It's good for neither A nor B.
It's not good for either A or B.
But sentences 3 and 4 are too stilted for casual day-to-day speaking purposes.
For reasons not obvious to me, sentence 1 sounds more "correct". Maybe because the conjunction or is also used in sentences 3 and 4, which are very familiar structures.
Specific Context-based Question
Which conjuction should I use in this case?
NRF of 200 N is acting upwards and weight of 200 N is acting downwards. But the object is not moving in either of these two directions. Therefore, no work is done by NRF ___ weight.