1) When adding the 2^n'th element. Linked List would just append to the tail O(1) time where as ArrayList would double the size copy half the array and then add it doing O(N) amount of work. Still though amortized analysis of insertions in array list is O(1) because rarely do we double the size of array.
(30 times required to double the array for insertion of a billion elements).
(30 times required to double the array for insertion of a billion elements).