Properties of Bulk Matter Questions and Answers

Answer: C

(A) is true, but (R) is false.

Ice does float on water. The reason is density: when water freezes, hydrogen bonds hold the molecules in an open hexagonal lattice, so ice takes up about 9% more volume than the same mass of liquid water and is less dense. An object less dense than water floats.

Ice does not 'combine with surrounding air' to gain buoyancy. Clear ice with no trapped air still floats, so the reason given is false.

Answer: D

The mass is 144 g.

Density is mass per unit volume, so mass is density multiplied by volume:

\[ \begin{aligned} m &= \rho \times V \\ &= 24\ \text{g/mL} \times 6\ \text{mL} = 144\ \text{g} \end{aligned} \]

The units confirm it: g/mL multiplied by mL leaves grams. The other options (142, 143, 146 g) are near-misses from multiplication slips.

Answer: A

The correct statement is that an object that floats in liquid C may or may not float in liquid A.

An object floats in a liquid if its density is less than the liquid's. An object floating in C (924 kg/m³) has density below 924; it will also float in A (785) only if its density is below 785, so it may or may not.

The other statements fail. An object floating in A has density below 785, so it surely floats in the denser B; 'may or may not' is wrong. An object floating in B (below 820) need not float in the less dense A, and one floating in C (below 924) need not float in B (820).

Answer: C

A person does not drown in the Dead Sea because of the high density of sea water.

The Dead Sea contains so much dissolved salt, roughly ten times as much as ordinary seawater, that its density is far greater than that of fresh water and greater than that of the human body. By Archimedes' principle, a floating body displaces its own weight of liquid; in such dense water a person needs to sink only a little way to displace enough, so the person floats easily.

Low density would make sinking easier, not harder. The total volume of water does not affect whether something floats, and 'neither high nor low density' gives no reason at all.

Answer: B

The buoyant force acts in the upward direction.

Pressure in a liquid increases with depth, so the push on the bottom of an immersed object is greater than the push on its top. The net force, the buoyant force, therefore acts upwards, and by Archimedes' principle it equals the weight of the liquid displaced.

The sideways pressures cancel, so the force is not parallel to the surface, and it opposes the object's weight rather than acting downwards or in all directions.

Answer: D

The water will not spurt out of the hole because the pressure inside the bottle is less than the outside pressure.

With the cap closed, air is trapped above the water. As soon as a little water starts to leave through the hole, that trapped air expands into the extra space, and its pressure falls below the atmospheric pressure outside. The low air pressure inside, together with the outside air pushing on the hole, holds the water back, so at most a few drops come out and the flow stops.

If the cap is opened, air can enter from the top and the water spurts out. Options A and C say the water spurts, which happens only with the cap open, and option B gives the wrong reason: the pressure inside is lower, not higher.

Answer: C

The reason is the lowering of the boiling point of water at high altitudes due to decrease in atmospheric pressure.

Water boils when its vapour pressure equals the pressure above it. At high altitude the air pressure is lower, so water boils below 100 °C, and food in an open pan cooks slowly because the water never gets hot enough. A pressure cooker traps the steam, raising the pressure inside and with it the boiling point, so the food cooks faster.

The other options get the direction wrong: atmospheric pressure decreases, not increases, with altitude, and the boiling point falls, not rises.

Answer: A

Both balls displace the same amount of water.

A fully submerged object pushes aside a volume of water equal to its own volume. Statement (iv) says the two balls have identical volumes, so they displace equal amounts of water.

The densities and the fact that A is heavier only tell us how much each ball weighs; with A's density of 13600 kg/m³ and B's 7800 kg/m³, both are denser than water and sink, so both are fully submerged. Weight does not change the volume displaced, and every submerged object displaces some water.

Answer: C

It is difficult because the area of contact increases.

Pressure is force divided by the area over which it acts. A blunt edge touches the object over a larger area, so the same force produces less pressure and the knife does not cut easily. A sharp edge has a tiny contact area, so the pressure is large.

The pressure decreases with a blunt knife, so 'pressure increases' is wrong. The force applied does not depend on the edge, and the contact area grows, not shrinks, when the knife is blunt.

Answer: C

(A) is true but (R) is false.

Food cooks more easily at sea level, so the assertion is true. At high altitudes air pressure is lower, so water boils at a lower temperature, for example about 70°C near the top of Mount Everest. Food in boiling water there gets less heat and takes longer to cook, which is why pressure cookers are used in the hills.

The reason says the boiling point increases at altitude, which is the opposite of the truth, so it is false.