Matric Notes Physics 9th Ch 7 Properties of Matter Short Questions

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Q.1) If you climbed a mountain carrying a mercury barometer, would the level of mercury in the glass tube of the barometer increases or decreases as you climb the mountain? Explain.

Answer: As we climb up the mountain the level of mercury in the glass tube of the barometer decreases.

The height of the mercury column depends on the atmospheric pressure. A higher atmospheric pressure results in an increase of the height of the mercury column in the barometer and vice versa.

The atmospheric pressure decreases as we go towards the higher altitude, hence, the level of the barometer also decreases.

Q.2) Walnuts can be broken in the hand by squeezing two together but not one, why? 

Answer: When two walnuts are placed in the hand, the area of the palm of the hand is greater than the area of surfaces of walnuts in contact.

As we know                                        Pressure = Force/ Area

When a force is applied to squeeze these walnuts together, the pressure between the surfaces in contact increases as the contact area is small. Hence, by the above equation, a decrease in the area results in a higher pressure which causes the walnuts to break at the surface in contact.

Q.3) Why is the cutting edge of the knife made very thin?

Answer: The cutting edges of the knife are made very thin because the smaller the area more will be the pressure that is exerted on the area and vice versa.

Mathematically, we know the relation between pressure and applied force where ‘P’ is pressure, ‘F’ is the applied force and ‘A’ is area. Hence, a small area with large pressure is easy for things like cutting, slicing or stabbing etc.

Q.4) Why water tanks are constructed at the highest level in our houses? 

Answer: As we know that                                         p = ρgh

The water tanks are constructed at the highest level in our houses because the pressure depends upon the height.

From the above equation, the pressure of water increases with height. So as the pressure applied by the water on pipes increases it results in an easy flow of water in a pipe system.

Q.5) Why a small needle sinks in water and huge ships travel easily in water without sinking?

Answer: A small needle sinks in water while a huge ship travels easily in water without sinking because the density of needle is greater than water.

                F (buoyant force of fluid) = W (displaced fluid) = m (mass of fluid) x g

                                                       ρ  = m/V

The mass of needle is more than the mass of water having same volume. Hence, the density of the needle is greater than the density of water displaced by it. As a result the buoyant force of fluid is less than the weight of the needle, so the needle sinks in water.

In the case of a huge ship, the weight of water displaced is greater than the weight of the ship due to which the ship does not sink and floats on water.

Q.6) Explain how and why camels have adapted to allow them to walk more easily in desert conditions?

Answer: Camels can walk easily in the desert because of their wide feet. Their wide feet allow the weight of their body to act on a larger surface of land reducing the pressure exerted on the land by the camel. we know that pressure exerted and area are inversely proportional.

Q.7) You would have probably experienced your ears ‘popping’ while driving in mountains. Why ears’ pop’?

Answer: In our ears a fluid maintains the internal and external pressure normally. While driving to an elevation the change in the atmospheric pressure results in changing the pressure on the ear drums, so a net pressure arise on ear drums which cause popping.

It can be relieved in a few minutes or by swallowing, chewing or blowing out nose.

Q.8) If you filled an airtight balloon at the top of a mountain, would the balloon expand or contact as you descend the mountain? Explain.

Answer: The air balloon will contract as the atmospheric pressure increase going down the mountain. So the external pressure is more as compared to the pressure on the top of the mountain.

Q.9) A rowboat is floating in a swimming pool when the anchor is dropped over the side. When the anchor is dropped, will the water level in the swimming pool increase, decrease, or remain the same? Explain.

Answer:  When the anchor is dropped, the water level in the swimming pool increases as the anchor displaces a volume of water resulting in the water level to rise. In this case, the swimming pool attains more volume of the anchor as it is dropped in it.

Q.10) Which material is more elastic, steel or rubber and why?

Answer: Elasticity is defined as the ability to resist a change.

Steel is more elastic than rubber because steel produces more resistance against the deformation than rubber. So, more deforming force is required to deform steel while rubber can be easily deformed.