Why can't the name "Musa" be replaced by just an Alif such as the alif in "Sam‚" ( surat 79 verse 27) instead of a "Yaa"?

Assalamu Aleikum

1) I have noticed that the "yaa" and the "alif" are used to lengthen and determine long vowels such as in surat 81 verse 20:"dhii quwwa tin..." (using the yaa after the letter dhal) or surat 110 verse 1:"idha dj‚..." (using the alif for the mudood).
However, I have noticed that in the name "Musa" (Moses) in the Quran, for instance in surat 87 last verse, both the "yaa" and a small "alif" are written to lengthen the name. My question is: Why the name "Musa" cannot be replaced by just an Alif  such as the alif in "Sam‚" ( surat 79 verse 27) instead of a "Yaa"?

2) In surat 41 verse 44 in the second line there is an Alif followed but another alif. However the second alif carries a black dot (or black point). What is the significance of this? I know that this sort of mark on the alif can be found in the Qur'an written in Warsh (I have seen it) but I did not notice until today that Hafs had it too.
Would you please explain whether or not one should read this type of alif or not?

May Allah bless you all inshallah

Answer

Wa alaikum assalaam wa rahmatu Allahi wa barakatuh.

1. The alif maqsooraa is written as a  with no dots on it, and the addition of the small dagger alif is put in by the scholars to show it is pronounced as an alif, such as in    , and .  This alif was, in most cases, originally a  and has changed into an alif for grammatical or other reasons.  The qira’aat that have imaalah, such as the qira’ah of  and  make imaalah of this alif changed from a  in a large percentage of the cases.  As you may know, imaalah is part alif and part .  The alif maqsooraa then is indicative of an alif that has originated from a , and in many cases for some ways of recitation, this alif is read as a mixture of an alif and a .  

2. The word   in aayah 44 of surah Fussilat has a special symbol (i.e. black dot) over the second hamzah, to show it is read a special way in the recitation of Hafs ‘an ‘Aasim.  This second hamzah is read with , meaning in this word it is read with an “easing” of the hamzah so that it is in between a hamzah and an alif.  This is a word that is read different ways in the different qira’aat. Please also see: http://www.abouttajweed.com/that_what_is_needed_for_hafs_part_3.htm

May Allah bless you as well.

Wa assalaam alaikum wa rahmatu Allah.