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Depends how quickly it locks up
It really doesn't. Maximum deceleration, and hence maximum loading on the mounts, will occur before the front wheel locks up and the front tyre is right at the extreme of its grip circle before locking up. But any braking system which is powerful enough to lock up the front wheel will by definition be sufficient to reach maximum deceleration and hence maximum loading in the brake mounts.
Depends how quickly it locks up. If it happens quicker then you're exerting more force.