The Brainliest Answer!
Karate experts break a slab using a single blow because they reduce the time so that the force increases. and we know that force is directly proportional to rate of change of momentum and inversely proportional to the time taken. and one more reason is that it needs a lot of practice.
 since they do it very fast change of momentum is also very fast and thus force is also very fast.           
           hope that this will help u. 
2 5 2
Change of momentum is fast and that's why force is very high, not fast.
Nice answer!
wont that hurt our hand????
thanks...excellent answer