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Information about this web site => Question related to Physics or physics related simulation => Topic started by: luv2cris on December 10, 2008, 02:13:39 am



Title: 1600 lb bear
Post by: luv2cris on December 10, 2008, 02:13:39 am
A 1600 pound polar bear is floating in seawater, which has a density of 64 lbs/ft3.   1/2 cubic foot of bear is above water.  Find the volume of the bear. 

Now, what I did was take  mass = density X  volume    and I got v = 25 cubic feet.    My teacher says this is wrong because 1/2 cubic foot is above water.  I dont understand what difference that makes.  If I put an 8 cubic foot block into water or hold it above in the air, the volume doesnt change.  It's still going to be 8 cubic feet.  right?


Title: Re: 1600 lb bear
Post by: lookang on December 16, 2008, 02:02:53 pm
From the diagram (http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=815.0;attach=479)

allow acceleration =0

sum F = 0
 
upthrust = weight

Rowwater*g*Volumedisplaced= mass*g

64*g*[V - 0.5 ] = 1600*g

V = 25.5 ft^3 = Volume of solid (bear)


My assessment of your question:
Now, what I did was take  mass = density X  volume    and I got v = 25 cubic feet.
So you are saying the Volume bear is 25 ?
your mistakes are:
1. assume density of bear as density of water
2. use of formula mass = density*volume without the correct context

   
If I put an 8 cubic foot block into water or hold it above in the air, the volume doesnt change.  It's still going to be 8 cubic feet.  right?
your mistake is
1. lack of a diagram to help you visual and understand the problem

suggestion:
look at the way i solve the problem, do you see why i use
[V - 0.5 ] = Volumedisplaced ?


Title: Re: 1600 lb bear
Post by: Zhah001 on February 18, 2015, 07:01:04 pm
  WE WERE FACING NORTH AND THE RAINBOW THAT WE WERE LOOKING AT BEFORE WAS EAST OF US, AT OUR ELEVATION AND HIGHER .  I,M NOT EXACTLY SURE BUT I BELIEVE THAT IT WAS MID TO LATE AFTERNOON.  I DO KNOW THAT WHEN EVER I LOOKED AROUND , IN EVERY DIRECTION , THERE WERE COLORS. AND ABOVE ME I COULD SEE LARGE WIDE BANDS OF COLORS. I HAVE NO EXPLANATION JUST A REAL MAGNIFICENT EXPERIENCE !  WISH I COULD MEET SOMEONE WHO'S HAD THIS HAPPEN TO THEM ?  OF COURSE ANY FEEDBACK IS WELCOMED.