Apple Interview Question: If you and a large brick are ... | Glassdoor

Interview Question

Product Design Engineer Interview Cupertino, CA

If you and a large brick are in a boat floating in a pool

  , will the water level rise or fall when the brick is tossed into the water? What if the brick is a large piece of Styrofoam and thrown into the water?
Answer

Interview Answer

6 Answers

4

cannot believe Apple ask this kind of middle school physics question... The water level will not change.

Anonymous on Aug 2, 2011
52

Your answer indicated the necessity of this question.

Anonymous #2 on Oct 2, 2011
1

If the brick was the size of a pebble but very dense, the water level would rise since the pebble displaces minimal water compared to the boat. On the other hand, if the brick was large (perhaps even larger than the boat), less dense, and of the same weight as the pebble, the water level would rise.

Anonymous on Oct 16, 2011
46

The water level will decrease ( if the brick has a density greater than water, which of course a conventional brick does). When in the boat, the brick will displace a mass of water equal to it's own. So if it has a mass of 1kg it will displace 1kg of water. When thrown overboard it will now displace an amount of water equal to it's volume. As it sinks, it's density must be grater than water and therefore it's 1kg mass will take up a smaller volume than 1kg of water. Therefore the water level will decrease.
As a styrofoam brick has a lower density than water it will not sink when thrown overboard. When floating it will displace a mass of water equal to that of the brick and therefore the water level will remain the unchanged.

Clueless bob on Jun 2, 2012
2

A powerful tool in looking at questions like these intuitively rather than by the raw physics is to go to the extreme. Say the brick were of normal brick size but were made of some ultra-dense material...so dense that it would push an aircraft carrier down in the water to the brink of sinking. This would obviously cause the carrier to displace many thousands of gallons more water than it had been displacing before the brick was added. When the brick is thrown overboard, the carrier would come shooting up out of the water, now not displacing those additional thousands of gallons of water The volume of water displaced by the brick once it's in the water is comparatively insignificant. So clearly the water level will fall.

Anonymous on Apr 21, 2016
0

To similarly answer the styrofoam question, take my aircraft carrier example but say the brick were suspended on an infinitely thin (no weight or volume), super strong wire below the carrier. Nothing would change because the volume of the brick and wire are still insignificant compared to all the water the carrier would still be displacing, but the weight of the brick is still pulling the carrier down. If you then cut the wire, the brick would sink and the carrier would go shooting up. No difference here.

But now say you do the same thing with styrofoam. You initially have the block in your hands on the boat, attached to an infinitely thin wire attached to the bottom of the boat. You throw the block overboard, and it floats. In this case, nothing has changed...the block is still part of the boat, connected by the wire. Remember, the water displaced by a boat is purely a function of its mass, so its configuration is irrelevant...we still have a single object here. Since nothing has changed, the water level won't be affected. Now cut the wire, making the block no longer part of the boat. The block is now fully "thrown overboard", the act of cutting the wire clearly does not change anything, and so again nothing will change.

Anonymous on Apr 21, 2016

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