Question

what does u=0 means?​

Answer 1

U = 0 basically means that all your values in one sample are larger than all the values in the other, a very extreme situation where you can reject the null hypothesis that the samples have been drawn from the same distribution (even for relatively small samples as yours)

Answer 2

Answer:

The value in one sample are larger than then all the values in the other, a very extreme situation where you can reject the null hypothasus.