Question

if one cut wrist they die but when whole arm is cut person survives why??

Answer 1

because in case of wrist main artery is damaged

Answer 2

in case 1 due to the damage of the artery  as it is much closer to the epithelial layer than any part of the body ,the blood hemorrhage is quiet significant n the person dies of hemorrhage ... here blood is still circulating in the rest of the arm 
in case 2  the blood supply to the arm is cut of no blood enters the heart form the cut arm hence person has more chances of surviving