Monday

December 22, 2014

December 22, 2014

Posted by **sand** on Monday, December 26, 2011 at 11:44am.

a) What fraction of the lead brick’s volume is above the surface of mercury?

A student uses a stick to push the lead brick below the mercury surface so that it is completely submerged. What force is required to hold the lead brick below the mercury surface?

- physics -
**drwls**, Monday, December 26, 2011 at 12:09pmYou need to know the specific gravity (or density) of both lead and mercury to answer this question.

Lead has a specific gravity of 11.35, so it is 11.35 times as dense as water. It's density in SI units is

rho1 = 11.35*10^3 kg/m^3

Mercury has a specific gravity of 13.56 and density

rho2 = 13.56*10^3 kg/m^3

The buoyancy force is (rho2)*g*V'

where V' is the displaced volume of mercury. The brick's weight is W = (rho1*g*V)

where V is the volume of the brick.

Setting them equal,

V' = (rho1/rho2)*V = 0.837

The fraction above the surface must be 0.163 or 16.3%

To hold it all beneath the surface, the force required is (rho2 - rho1)*g*V =

2.21*10^3*9.8*7*10^-4 = 15.2 N

- physics -
**sand**, Monday, December 26, 2011 at 6:53pmThanks a lot

**Answer this Question**

**Related Questions**

physics - A lead brick with volume of 7*10^-4m^3 is floating in bath of liquid ...

Physics - Find the heat that flows in 1 s through a lead brick 18 cm long if the...

Physics - Hi maybe someone can help me out, since my teacher isn't available ...

physics - An iron cube floats in a bowl of liquid mercury at 0 C. a) If the ...

Physics - The relative density of mercury is 13.6. Find the ratio of the mass of...

bio physics - A 2.80kg block of copper with a height of 0.250m and an area of 1....

Physics - A 3.0 kg brick rests on a perfectly smooth ramp inclined at 34 above ...

Physics - A 3.0 kg brick rests on a perfectly smooth ramp inclined at 34 above ...

Physics - A 3.0 kg brick rests on a perfectly smooth ramp inclined at 34 above ...

Physics - A 3.0-kg brick rests on a perfectly smooth ramp inclined at 34° above ...