I’m not really sure I’m sorry
Answer:
Explanation:
The stunt will likely sustain serious injury in case of concrete blocks because the average force acting on the person will be more because concrete blocks do not squeeze to provide more time for the force to act on the body instead it acts for a small amount of interval.

As impulse is constant so time requires to act force on the body is more as compared to concrete block and thus average force in mattress case is less.
Rate of speed (3 m/s north is three miles per second north, so it's a rate of speed)
The water molecules with a slower speed are escaping