River rock

Question 1

(a) Any four: measure mass of the (dry) rock with a balance [1]; fill eureka can until it overflows / wait until dripping stops [1]; place empty measuring cylinder under the spout [1]; lower rock fully on a thread / collect overflow [1]; volume of overflow $=$ volume of rock [1]; mention repeats / meniscus / no air bubbles [1] (max 4)

(b) $m=0.180\,\text{kg}$ and $V=7.5\times 10^{-5}\,\text{m}^3$ [1]; $\rho=m/V=2400\,\text{kg/m}^3$ [1]. Allow $2.4\,\text{g/cm}^3$ converted correctly.

Question 2

(a) $p=F/A$ [1]; $400/0.0020$ [1]; $2.0\times 10^5\,\text{Pa}$ [1]

(b) $p=h\rho g$ [1]; $4.0\times 1000\times 10$ [1]; $4.0\times 10^4\,\text{Pa}$ [1]. Do not require atmosphere — the question asks for the difference due to the water.

Question 3

(a) Particles move randomly / in all directions [1]; collide with the walls [1]; each collision exerts a force / force per unit area is pressure [1]

(b) Particles move faster / greater average KE [1]; collide more frequently and/or with greater force [1]; pressure increases [1]

Question 4

(a) $p_1V_1=p_2V_2$ [1]

(b) Substitution $100\times 40=p_2\times 20$ [1]; $p_2=200$ [1]; kPa [1]. Allow $2.00\times 10^5\,\text{Pa}$.

(c) Smaller volume / particles closer together [1]; more frequent collisions with the walls [1]; greater force per unit area so pressure increases [1]. Reject “particles move faster” if offered as the only reason (temperature is constant).