Because I’m procrastinating at work:

How many sessions of coitus might it take to accumulate 5 km of cock thrusts?

Estimates:

• average erect length: 13 cm (from Perplexity.ai)
• average number of thrusts in coitus: 300 (ibid)

Calculations

• thrust distance per coitus session: 13 cm x 300 thrusts x 2 (accounting for insertion & removal) = 78 m
• coitus sessions to accumulate 5 km of thrusts: 5 km / 78 m = 64.1 -> 64 sessions of coitus

So OP’s wife would have to fuck 64 times to accumulate 5 km of cock. Even with amazing refractory periods, that’s still a minimum of 32 guys running a train on her.

Edit: working through this reminded me of that episode of HBO’s Silicon Valley where they started talking about handjobs and hotswapping dicks and hit on middle out compression.