If you block someone on Facebook,will they know? Will they be able to find out you blocked them?

To make a long sotry short, my mom doesn't know i have a fb, and if she does, i will not be able to walk again. And fb helps me with school, and i've met some pretty cool people on it.. Anyways, if i block her will she be able to find out, and yes i am sneaky, and yes this is very... childish :P
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