hebrew - Why is the word שמך vocalized differently in different places?

Gen 32:29 says:

וַיֹּאמֶר, לֹא יַעֲקֹב יֵאָמֵר עוֹד שִׁמְךָ...‏

Thy name shall be called no more Yaakov...

But in 30 it says:

וַיִּשְׁאַל יַעֲקֹב, וַיֹּאמֶר הַגִּידָה-נָּא שְׁמֶךָ,...‏

And Yaakov asked him, and said: 'Tell me, I pray thee, thy name.' ...

"Your name" is vocalized differently between the two. Why do we sometimes read shimkha and sometimes shmekha?