Seawater

Question 1

(a) Measure mass with a (top-pan) balance [1]; measure length, width and height with a ruler / callipers (repeats / mean) [1]; $V=lwh$ and $\rho=m/V$ [1]

(b) $V=8.0\times 4.0\times 2.0=64\,\text{cm}^3=6.4\times 10^{-5}\,\text{m}^3$ [1]; $m=0.173\,\text{kg}$ [1]; $\rho=2700\,\text{kg/m}^3$ [1]. Allow $2.70\times 10^3$.

Question 2

(a) $p=h\rho g$ [1]; $2.5\times 1020\times 10$ [1]; $2.55\times 10^4\,\text{Pa}$ [1]

(b) Adds atmospheric pressure [1]; $1.255\times 10^5\,\text{Pa}$ [1]

(c) Equally in all directions / in every direction [1]

Question 3

(a) Pressure is force per unit area / $p=F/A$ [1]

(b) Particles in a smaller volume / closer together [1]; they collide with the walls more frequently [1]; (average speed unchanged because $T$ is constant) [1]; greater force on a given area so pressure increases [1]

(c) Boyle’s law [1]

Question 4

(a) $293\,\text{K}$ [1]; $373\,\text{K}$ [1]

(b) $p_1/T_1=p_2/T_2$ or $p_2=p_1 T_2/T_1$ [1]; $120\times 373/293$ [1]; $153\,\text{kPa}$ (allow $152$–$153$) [1]

(c) $p$ is proportional to absolute temperature / $p=0$ at $0\,\text{K}$ not at $0^\circ\text{C}$ [1]; using °C would give a wrong ratio (e.g. $100/20$) [1]