WAEC Physics 2018 Paper

Let $h_{Q}$ and $\rho_{Q}$ be the least length and the density of $Q_{1}$

while $h$ and $\rho$ are the length and density of mercury respectively.

$h \times \rho \times g = h_{Q} \times \rho_{Q} \times g$

$76\,\mathrm{cm} \times 13.6 \times 10 = h_{Q} \times 16.2 \times 10$

$h_{Q} = \frac{76\times 13.6\times 10}{16.2\times 10}$

$h_{Q} = \frac{10336}{162}$

$h_{Q} \approx 63.8\,\mathrm{cm} = 638\,\mathrm{mm}$