There is often confusion over the words passed and past. Here follows grammarmonster.com's article to help you figure out which one goes where.
Passed
The word passed is the past tense of the verb to pass, e.g., I pass (present tense), I passed and I have passed (both past tense), and I will pass (future tense).
Examples:
"She passed the exam with distinction." (In this example, to pass = to be successful in a test)
"The operator has already passed the note to the typist." (In this example, to pass = to hand over)
"The lion passed the zebra without so much as a glance." (In this example, to pass = to move past)
To pass often means to move past, and this is where confusion can arise. Of note, to pass can also mean to sail past, to fly past, to run past, to hop past, etc. - the method of moving is irrelevant. This is worth bearing in mind because if you have used a verb indicating motion already, then it will be partnered with past and not passed. Remember, passed is the past tense of the verb to pass. This is a 100% rule.
The lion passed the zebra without so much as a glance. Correct
The lion wandered past the zebra without so much as a glance. Correct
The Harrier passed at an altitude of 100 feet. Correct
The Harrier flew past at an altitude of 100 feet. Correct
Past
The word past has several meanings (usually related to time before the present or to indicate movement from one side of a reference point to the other side.) Past can be used as an adjective, an adverb, a noun or a preposition:
As an Adjective, past denotes time before the present.
"This past year has been difficult for the recruiters."
"She loves to tell us about past dance competitions in the hall."
As a Noun past means the time before the present.
"That's all in the past."
"Can you dig into his past?"
As an Adverb, past means beyond or denotes movement from one side of a reference point to the other.
"Don't go past."
"Alan ran past."
(Note: The word past is acting as an adverb in each of these examples. However, it could be argued that the word past is a preposition forming part of phrasal verb (like to run away or to jump up). See the similar examples below.)
As a Preposition. As a preposition, past means beyond or denotes movement from one side of a reference point to the other.
"Don't go past the gate." (past = beyond)
"Alan ran past the postman." (past = denotes movement from one side to the other)
P.S I hope that's been somewhat useful folks, but pop any questions below and I shall endeavour to assist.