[jp.101]

Hi i am a Biology Student and its really giving me problems this one, can someone help?

"A string supports a solid iron object of mass 180g totally immersed in a liquid of density 800kgm-3. Calculate the tension of the string if the density of iron is 8000kgm-3"

I am confused here, Archimedes principle for immersed bodies states that downward force - upward force = net force , is net force tension? With these parameters is is possible to calculate the tension?

One of my assumptions on this is that the string weight is ignored.

JP

[enahs]

Yes you ignore the weight of the string.

What would the tension of the string be if it was hanging not in water?
What is the upwards "force" due to buoyancy?
What is the difference?

[Astrokel]

Hi, just to add bit from the hints given by enahs already. When approach forces problems, it is always wise to draw a free body diagram.

[nj_bartel]

archimedes' principle

[macman104]

archimedes' principle

And...

I am confused here, Archimedes principle for immersed bodies states that downward force - upward force = net force , is net force tension? With these parameters is is possible to calculate the tension?

[jp.101]

i think i got it....

another assumption which may be obvious is that its at rest so external forces acting upon this is zero.


T = m (iron) x g - m (volume of liquid displaced by iron) x g

thanks for the help

[nj_bartel]

archimedes' principle

And...

I am confused here, Archimedes principle for immersed bodies states that downward force - upward force = net force , is net force tension? With these parameters is is possible to calculate the tension?

Oops! Sorry, somehow skimmed over that.

Your setup is correct.  One thing - a system doesn't have to be at rest for there to be 0 net force on it.  There must be no acceleration for there to be 0 net force; that doesn't mean that the object couldn't be, say, sinking with constant velocity.