Jul 14, 2009
2
0
Status
Pre-Health (Field Undecided)
i have a practice question i can't seem to figure out.

A cube 5m a side, specific gravity .8, is suspended by a robe so 1 m is submerged in a liquid with specific gravity of .4. What is the tension in the rope?

So I think buoancy is probably a factor. but really Im lost in all of these types of questions.

Any help would be appreciated!
 
May 8, 2009
289
1
Status
Pre-Medical
Hopefully I did the math right...

F(g) and F(b) point opposite
F(g) and F(t) point opposite

Fg = Ft + Fb

Fg = (mass) x (gravity) or (density)x(volume)x(gravity)
density object = (.8)(1000) = 800
volume object = (5x5x5) = 125
gravity = 10

Fb = (fluid density)x(volume submerged)x(gravity)
density fluid = 400
volume submerged = (1x1x5)
gravity = 10

Fg - F = Ft
(800)(125)(10) - (400)(5)(10) = Ft

1,000,000 - 20,000 = 980,000 = 9.8 x 10^5 N

Is the rope attached to the ground or is it in the air, how is this thing hanging or floating or what ever. O well I think my math is right if the rope is attached to the top of the cube and aiding the force buoyant.
 
Last edited:

Tutmos

MS0
10+ Year Member
Apr 10, 2008
533
1
Status
Medical Student
Hopefully I did the math right...

F(g) and F(b) point opposite
F(g) and F(t) point opposite

Fg = Ft + Fb

Fg = (mass) x (gravity) or (density)x(volume)x(gravity)
density object = (.8)(1000) = 800
volume object = (5x5x5) = 125
gravity = 10

Fb = (fluid density)x(volume submerged)x(gravity)
density fluid = 400
volume submerged = (1x1x5)
gravity = 10

Fg - F = Ft
(800)(125)(10) - (400)(5)(10) = Ft

1,000,000 - 20,000 = 980,000 = 9.8 x 10^5 N

Is the rope attached to the ground or is it in the air, how is this thing hanging or floating or what ever. O well I think my math is right if the rope is attached to the top of the cube and aiding the force buoyant.

You got your math wrong. The volume submerged is 5x5x1 not 5x1x1 resulting in 900,000 N not 980,000 N.