The Riddle

P

PAUL XAVIER

Junior Member
Joined
Apr 1, 2014
Messages
14
Reaction score
0
Location
chennai
I think its worth a try!

A man stuck in a small sailboat on a lake throws a stone overboard. It sinks to the bottom of the lake.What will happen to the water level of lake?
PS:Lake is not large enough to neglect the effect of stone.
 
OK, well, while the rock is in the boat it displaces more than its volume, through the agency of the boat, when it sinks, it displaces exactly its volume, so I'd say the level of the lake falls.
 
Mr Efficiency said:
OK, well, while the rock is in the boat it displaces more than its volume, through the agency of the boat, when it sinks, it displaces exactly its volume, so I'd say the level of the lake falls.
Click to expand...

Concur. The water level in the lake falls proportional to the water volume density equal to the weight of the rock (i.e. boat displaces less). The water level in the lake rises proportional water volume density of the volume of the rock. Since the rock sinks, the rock volume * the water volume density is less than the rock weight, so the volume increase is less than the volume decrease so the total volume (water +rock) is less than the previous volume (water+boat)

Is your homework going well?
 
I would say the level stays the same
When the rock is in the sailboat, the sailboat displaces the weight of the rock and the boat.
Two conditions
When the rock is in the air before it hits the water, the lake level drops as the boat displaces only the weight of the boat

When the rock is under water, the lake level comes up to its original level
 
When the rock is on the bottom of the lake it displaces only its volume. When the rock is in the boat it displaces its weight via the boat hull. The lake level drops, more or less, depending upon the surface area of the lake. The greater the area, the more insignificant the variance.
 
when the stone is in the boat it displaces its *weight* of water.

when it is in the air it displaces no water

when it is in the water it displaces its *volume* of water.

the weight of the stone's volume of water is less than the stones weight of water.

(we know that because it sinks)

So, as the stone is tossed out of the boat, the level will go down, then come back up as the stone enters the water, but not as far up as it did when it was in the boat.

You can see this demonstrated in the following video from about 2.35 on.



ok, it doesn't really demonstrate it at all, but hey its related, and if you don't know it, its such a glorious short that its worth watching the whole thing :P
 
There is no change. The boat, lake and stone comprise a closed system.
 
PAUL XAVIER said:
A man stuck in a small sailboat on a lake throws a stone overboard. It sinks to the bottom of the lake.What will happen to the water level of lake?

PS: Lake is not large enough to neglect the effect of stone.
Click to expand...

Same kind of question was asked before, the lake's water level drops . . :idea:

P.S. - See post #22 & #24 for the explanation there.
 
As a thought experiment, assume the 'stone' is made of whatever a neutron star is made of (extremely high density), and thus is microscopic in volume. How will throwing it overboard change, or not change, the level of the lake?
 
ImaginaryNumber said:
As a thought experiment, assume the 'stone' is made of whatever a neutron star is made of (extremely high density), and thus is microscopic in volume. How will throwing it overboard change, or not change, the level of the lake?
Click to expand...

The same result, presumably, if the boat doesn't sink first !
 
Why postulate on the ridiculously impossible?
 
You must log in or register to reply here.
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making any potentially dangerous or financial decision, always employ and consult appropriate professionals. Your circumstances or experience may be different.

    • Back
    Top