To determine if the vowel is long when you are reading, look for the silent “e”. When a word ends in an e, the vowel before it is pronounced long. For example:
A: short a…cap long a with the silent “e” rule…cape
E: short e…pet long e with the silent “e” rule…Pete
I: short i…pin long i with the silent “e” rule…pine
O: short o…not long o with the silent “e” rule…note
U: short u…cut long a with the silent “e” rule…cute