U is usually pronounced as long vowel /yoo/ as in university if it is followed by consonant + vowel. For example, unit, utility, user, usual etc
Rule 1: U + consonant + vowel = yoo
U is pronounced as a short vowel /u/ as in uncle if it is followed by two consonants. For exmample, upper, under, updated, urban etc
Rule 2: U + consonant + consonant = u
Notice: The prefix un- (for adjectives) is always pronounced /u/ not /yoo/
an unanswered question
an unpleasant surprise
an unreal story
ليتهآ بالعربي !!
عسسب افهم 
عمؤمـآ
يزاج الله خير الغلـآ =)
شرح رائع وواضح
جزاك الله خيرا وفي ميزان حسناتك إن شاء الله