Yahoo Interview Question: Why is a man hole cover round... | Glassdoor

Interview Question

Customer Service REp Interview New York, NY

Why is a man hole cover round?


Interview Answer

9 Answers


Weight displacement. So the cover does not fall into the hole no matter where it is or what is on it.

Interview Candidate on Apr 3, 2009

There are a few answers that would qualify as "correct", but I suspect this question won't be making the rounds much longer as this is becoming the stereotypical case example question which is meant to "see how you think".

A circular manhole cover can never fall into the hole, as a square cover could by turning it on a diagonal, for example.
Also, a worker can easily roll the cover without every having to lift it.

Adam on Aug 19, 2009

In addition to Adam's answers, they are also round because they will fit on the manhole regardless of which way you put them on.

Tim on Jan 13, 2010

The real reason manhole covers are round is because the manhole is round. It certainly wouldn't do to put a square cover on a round hole. (However, that's likely not the answer they are looking for.)

Dave on Jan 17, 2010

Because the manhole pipe is round.

Maryann on Jan 18, 2010

Because if it were star-shaped it would have pointy bits that would be ouchy and tear your clothing.

Jeff in Boston on Jan 18, 2010

In addition to Adam's observations (which contain the very best answers to this question), a round manhole cover has no sharp corners, so if for any reason it did not sit right in the manhole, and a car or truck ran over it, it would be less likely to puncture the vehicle's tire.

KC on Jan 18, 2010

This was a Microsoft interview question at one point. It is round so that the cover can't fall into the hole the way a square or rectangular cover could if inserted diagnally. It's also easier to move (by rolling it).

CN on Jan 18, 2010

It's also the maximum coverage for the minimal amount of material - making it the cheapest shape in terms of material cost.

Tim on Jan 19, 2010

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