Viva Voce: Pressure | Extra Documents & Tests for Class 9 PDF Download

Q.1. Give the S.I. unit of thrust.

Newton

Q.2. State the S.I. unit of pressure.

Pascal (Pa).

Q.3. What is the blood pressure of a normal human being?

It is 120/80 mm of mercury. The blood flows in the vessels by a pressure that it can withstand.

Q.4. Define thrust.

The force acting on a body perpendicular to its surface is called thrust.

Q.5. Define pressure.

Thrust exerted per unit area is called pressure.

Q.6. What is one pascal?

When a force of 1 N acts on a surface area of 1 m² then the pressure is said to be one pascal.

Q.7. How are pressure, force and area related to each other?

Pressure = Force/Area, If force increases the pressure exerted also increases. If the area decreases the pressure increases.

Q.8. Give three examples where we have decreased the area to increase the pressure.

(i) knife
(ii) thumb pins
(iii) needle

Q.9. A cuboid of mass 5 kg and dimensions 5 x 10 x 20 cm is given, how will you place it so that
(i) maximum pressure is exerted and
(ii) minimum pressure is exerted?

(i) To get maximum pressure minimum contact surface area should rest. i.e. 5 cm x 10 cm.
(ii) To get minimum pressure the maximum surface area of cuboid should be in contact. i. e. 10 cm x 20 cm

Q.10. What happens to the gases if pressure is exerted on it?

On increasing the pressure on gases, it gets compressed.

Q.11. A body with dimensions 1 cm x 2 cm x 3 cm is placed on sand with three different surfaces. In which case the thrust exerted is more?

The thrust exerted by the surface of dimension 1 cm x 2 cm will be more, because it has least area than 2 cm x 3 cm and 1 cm x 3 cm surfaces.

Q.12. Why do nails have pointed tips?

The pointed tip of nail reduce the surface area, so that the force exerted by it on wall while hammering result in higher pressure and fixes in the surface.

Q.13. Give three examples where we have increased the area to reduce the pressure.

(i) Wider walls of dams
(ii) Broad straps of a bag
(iii) Broader and more tyres in loaded trucks

Q.14. A bottle is filled with water it has three points A, B and C as shown in the figure, at which point the pressure exerted is maximum.

The pressure is maximum at point C, because it has maximum depth.

Q.15. Why does railway tracks have wooden planks under it?

On the railway track, trains keep moving with pressure being exerted everytime and this pressure is distributed to wider area by the planks so that the tracks do not sink into the surface.