Rack (RAK)
Meaning 1: A wind-driven mass of high often broken clouds
Example Sentence: The rack of clouds seemed like cotton – wool floating in the sky.

Meaning 2: An instrument of torture on which a body is stretched
Example Sentence: The night spent out in the open was like spending a night on the rack.

Meaning 3: A frame or shelf often formed of a bar, that is used to hold things.
Example Sentence: They had beautiful carved shoe rack.

Wrack (RAK)
Meaning 1: The violent destruction of a structure, machine, or vehicle.
Example Sentence: They silently watched the wrack lined on the shore.

Meaning 2: Dried seaweeds.
Example Sentence: The sea wrack was sold in the shops on the harbor.

Meaning 3: To utterly ruin.
Example Sentence: The human body can withstand only a certain amount of wrack and strain.

Example Sentences using both the words
The sky was pale blue after the rack of clouds had blown off, but instead of feeling joyful I was wracked with pain.