Question

Take the density of the crown to be ρc. What is the ratio of the crown's apparent weight (in water) Wapparent to its actual weight Wactual ?
Express your answer in terms of the density of the crown ρc and the density of water ρw .
Wapparent/Wactual=____________

Answer 1

Concepts and reason The concepts required to solve the given questions is apparent weight and the actual weight. Initially, calculate actual weight of the crown. Later, calculate the apparent weight of the crow. Finally, express the answer in terms of the density of crown and the density of water.

Fundamentals The expression for the actual weight of the crown is as follows:

\(W=m g\)

\(=\rho_{c}\)

Here, \(\rho_{\mathrm{c}}\) is the density of the crown, \(\mathrm{m}\) is the mass, and \(\mathrm{g}\) is the acceleration due to gravity. The expression for the apparent weight of the crown is as follows:

\(W_{\mathrm{a}}=W-F_{\mathrm{B}}\)

Here, \(F_{\mathrm{B}}\) is the force of buoyancy. The expression for the buoyance force is given by, \(F_{\mathrm{B}}=\rho_{\mathrm{w}} V g\)

Here, \(\rho_{\mathrm{w}}\) is the density of the water and \(V\) is the volume, and \(\mathrm{g}\) is the acceleration due to gravity.

Substitute \(\rho_{\mathrm{w}} V g\) for \(F_{\mathrm{B}}\) in the equation \(W_{\mathrm{a}}=W-F_{\mathrm{B}}\). \(W_{\mathrm{a}}=W-\rho_{\mathrm{w}} V g\)

Rearrange the above equation as follows:

\(\frac{W_{\mathrm{a}}}{W}=1-\frac{\rho_{\mathrm{W}} V g}{W}\)

The density is equal the mass divided by the volume. It is denoted by \(\rho\). The force of buoyancy is directly proportional to the density of the water, volume, and acceleration due to gravity.

Substitute \(\rho_{\mathrm{c}} V g\) for \(\mathrm{W}, \rho_{\mathrm{w}} V g\) for \(F_{\mathrm{B}}\) in the equation \(\frac{W_{\mathrm{a}}}{W}=1-\frac{\rho_{\mathrm{W}} V g}{W}\).

$$ \begin{aligned} \frac{W_{\mathrm{a}}}{W} &=1-\frac{\rho_{\mathrm{w}} V g}{\rho_{\mathrm{c}} V g} \\ &=1-\frac{\rho_{\mathrm{W}}}{\rho_{\mathrm{c}}} \end{aligned} $$

Buoyant force is the upward force exerted on the object placed in the fluid.

The ratio of the crown's apparent weight to its actual weight is equal to \(1-\frac{\rho_{\mathrm{w}}}{\rho_{\mathrm{c}}}\).

Answer 2

1-(Pw/Pc)   Note: P is in place of the symbol rho.