iGCSE Physics (0625) 1.4 Density-Exam Style Questions- New Syllabus
▶️ Answer/Explanation
Detailed solution:
To find the volume of an irregularly shaped object, the displacement method is used. A ruler cannot be used because the object lacks regular dimensions to calculate volume via a formula. A balance measures mass, not volume. By immersing the rock in a measuring cylinder containing a known volume of water $V_{1}$, the water level rises to $V_{2}$. The volume of the rock is then calculated as $V_{rock} = V_{2} – V_{1}$. Therefore, only the measuring cylinder is required to determine the volume.
▶️ Answer/Explanation
Detailed solution:
An object floats if its density is less than the density of the liquid ($\rho_{object} < 0.95\text{ g/cm}^{3}$).
Density is calculated using $\rho = \frac{m}{V}$, where $V = 30\text{ cm}^{3}$ for all balls.
For P: $\rho_{P} = \frac{15\text{ g}}{30\text{ cm}^{3}} = 0.50\text{ g/cm}^{3}$ (Floats).
For Q: $\rho_{Q} = \frac{25\text{ g}}{30\text{ cm}^{3}} \approx 0.83\text{ g/cm}^{3}$ (Floats).
For R: $\rho_{R} = \frac{35\text{ g}}{30\text{ cm}^{3}} \approx 1.17\text{ g/cm}^{3}$ (Sinks).
For S: $\rho_{S} = \frac{45\text{ g}}{30\text{ cm}^{3}} = 1.50\text{ g/cm}^{3}$ (Sinks).
Since only P and Q have densities lower than $0.95\text{ g/cm}^{3}$, they are the balls that will float.
▶️ Answer/Explanation
Detailed solution:
Density is defined by the equation $\rho = \frac{m}{V}$, requiring both mass and volume.
While mass is measured using a balance, the volume $V$ of an irregular object cannot be calculated using a ruler.
Instead, the volume is found via the displacement method, where the stone is submerged in a liquid.
A measuring cylinder is essential to observe the change in liquid level, which equals the stone’s volume.
Other tools like a stop-watch (time) or voltmeter (potential difference) are irrelevant to this physical measurement.
Therefore, the measuring cylinder is the only useful piece of equipment listed for this specific task.