Answer:
right after jumping so 0s and as it falls its speed will keep increasing
Explanation:
If you mean work out as in using calculations, I don't know how to help you. But there is a way to find out, using Fleming's left hand rule. I can't define it properly, and I don't want to copy-paste from another site, so I strongly recommend that you look it up. Try google, or more specific, BBC GCSE bitesize.
Hope this helps!