cut and cuts subject verb agreement?

Question

As per the subject-verb agreement, if a subject is singular, its verb must also be singular

He sings.

if a subject is plural, its verb must also be plural.

They sing.

I have seen some examples of "cut" on the internet that created some confusion.

• Tom has cut his finger.
• Tom often cuts classes. (Tom is singular - so cuts are used)
• Tom cut classes again. (why is cut used here and not cuts. Tom is singular)

• My mother cut the cake.

  (My mother is singular, then shouldn't we use cuts here)

• This knife cuts well.

  (knife is also singular)

• Each cone cuts out an area on the surface equally inclined to the cone axis.

Answer 1

Notice that the distinction you made applies to the third person of the present simple tense.

You have a mixed collection of different tenses in your examples:

• Tom has cut his finger - PRESENT PERFECT tense - cut is the past particicle. The same past particle is used for all subjects

• Tom often cuts classes - PRESENT SIMPLE tense

• Tom cut classes again and My mother cut the cake - PAST SIMPLE tense - the same word is used for all subjects

Your two last examples are PRESENT SIMPLE tense too, cuts applies to both of them because they use the third singular person: it.