Cummins Interview Question: You are in a boat which is in... | Glassdoor

Interview Question

Service Engineering Intern Interview Columbus, IN

You are in a boat which is in the middle of a pond and you

  are holding a rock in your hand. You throw the rock into the lake. Does the water level of the lake rise?
brain teaser

Interview Answer

6 Answers


No right or wrong answer. They just want to see how you think.

Interview Candidate on Apr 18, 2012

The water level will drop. When you hold the rock, the extra displaced volume of water equals the weight of the rock. When you throw the rock into the lake, displaced volume is the size of the rock, which is less.

banmuyuan on Apr 20, 2012

both wrong. the water level does not change. at first the density the boat has is density of the boat + density of rock affecting water level. in the final situation the boat has gotten rid of the rock's density, but the rock (and its density) have been added to the lake, so we still have density of boat + density of rock affecting water level. location doesn't change physics.

Anonymous on Oct 20, 2012

The water level decreases when the rock leaves your hand, then increases again when the rock enters the water.

Anonymous on Oct 19, 2014

Does the final answer depend on the rock's density compared to the density of water?

Anonymous on Oct 22, 2014

While the rock is in the boat the displaced water has the same weight as the rock when the rock is in the water the volume of water displaced is the same as the volume of the rock. So the level of the water rises or falls depending on the density of the rock

Grazia Fadarishan on Feb 10, 2016

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