Force and pressure Sample paper

Q1. Which experiment demonstrates the power of atmospheric pressure?

Solution

Magdeburg hemispheres experiment demonstrates the power of atmospheric pressure.

Q2. When the nozzle of a syringe is dipped in a liquid and its piston is withdrawn, the pressure inside the syringe is

Solution

When the nozzle of a syringe is dipped in a liquid and its piston is withdrawn, the pressure inside the syringe is lowered.

Q3. Electrostatic force is the phenomenon that results from slow moving or stationary

Solution

Electrostatic force is the phenomenon that results from slow moving or stationary electric charges.

Q4. On the surface of earth, the atmospheric pressure is minimum at the sea level.

Solution

On the surface of earth, the atmospheric pressure is maximum at the sea level. As we go higher above the sea level, the atmospheric pressure decreases.

Q5. Which of the following cannot be accounted for atmospheric pressure?

Solution

Pins and nails are made with pointed ends because when force is applied on their head, it exerts a large pressure on the surface and pierces it and penetrates into it.

Q6. On what factor does the pressure exerted by water at the bottom of a container depends?

Solution

Pressure exerted by water at the bottom of a container depends on the height of the column.

Q7. Objects or things fall towards the Earth when left free. The force causing this free fall is

Solution

Earth’s gravitational force (force of gravity) pulls all objects towards its centre.

Q8. The pressure exerted by the atmosphere is

Solution

The pressure exerted by the atmosphere is equal to the pressure inside our body.

Q9. Every object in this universe, whether small or large exerts a force on every other object. What is the name of this force?

Solution

All objects in the universe exert a gravitational force on all other objects on account of their mass.

Q10. What is the direction of the frictional force acting between two bodies moving one over another?

Solution

Frictional force between two bodies moving one over another is always in the direction opposite to the direction of motion.

Q11. If the forces acting upon an object are balanced, then the object

Solution

When the forces are balanced, the net force is zero. As a result, if the object is at rest, it will remain at rest; and if it is moving with constant velocity, it will keep moving the same way.

Q12. How does a rubber sucker work?

Solution

When the rubber sucker is pressed against a flat, smooth surface, its concave rubber cup gets flattened to a large extent,  pushing out most of the air from beneath it. So the air pressure inside the rubber sucker becomes very low and the much greater atmospheric pressure acting on it from outside fixes the sucker firmly on the flat surface.

Q13. State an application where pressure is used to change the state of matter.

Solution

In LPG cylinders, pressure is applied on methane gas and it becomes liquefied. When it comes out from the holes of the burner, it is depressurized and it turns back into a gas which burns in the stove.

Q14. When more than one force acts on an object, the effect on the object is due to the _______ force acting on it.

Solution

When more than one force acts on an object, the effect on the object is due to the net force acting on it.

Q15. A magnetic force is

Solution

A magnetic force can be both attractive as well as repulsive. Like poles repel each other, whereas unlike poles attract each other.

Q16. The magnitude of non-contact forces

Solution

The magnitude of non-contact forces decreases with the increase in separation.

Q17. State the characteristics of liquid pressure.

Solution

The characteristics of liquid pressure are: 1) Liquid pressure increases with depth. 2) Liquid pressure remains the same in all directions at a given depth. 3) Liquid pressure depends upon the density of the liquid. 4) Liquid exerts pressure on the sides of the container. 5) A liquid seeks its own level.

Q18. What happens to the speed of the object if a force is applied on it in the direction of its motion?

Solution

Force applied in the direction of motion of an object increases its speed and force applied in the direction opposite to that of the motion of object decreases its speed.

Q19. When the air is compressed, it is said to be

Solution

When the air is compressed, it is said to be “under high pressure”.

Q20. Define the term pressure and state the unit of pressure.

Solution

Pressure is the force applied per unit area in a direction perpendicular to the surface of an object. It is also defined as thrust acting per unit area.  The unit of pressure is newton/metre2 (N/m2 or Nm-2), which is equal to 1 Pascal (Pa).

Q21. The Earth is surrounded by a layer of air upto a certain height and this layer of air is called _____________ .

Solution

The Earth is surrounded by a layer of air upto a certain height and this layer of air is called atmosphere.

Q22. In space, an object maintains its orbit due to the

Solution

In space, an object maintains its orbit because of the gravitational force between the object and the star or a planet around which it is revolving.

Q23. The force resulting due to the action of muscles in our body is known as

Solution

The force resulting due to the action of muscles in our body is known as muscular force.

Q24. What happens to the atmospheric pressure with the increase in height above the surface of the Earth?

Solution

With the increase in height above the surface of the Earth, the air pressure decreases because the column of air above us gets shorter.

Q25. How much is the air pressure on the surface of the Moon?

Solution

Air pressure on the surface of the Moon is zero as there is no air there.

Q26. Why some people feel their ears ‘popping’ at the top of a mountain?

Solution

At the top of a mountain, some people feel their ears ‘popping’ due to the decrease in air pressure. The ears pop in order to balance the difference in pressures outside and inside of the body.

Q27. If the area on which a force acts is small, it can produce large

Solution

Smaller the area, larger is the pressure for the same force. ( P = F/A)

Q28. When a rubber sucker is forced against a wall, the air between the sucker and the wall is forced out, creating a ________ in between.

Solution

When a rubber sucker is forced against a wall, the air between the sucker and the wall is forced out, creating a vacuum in between.

Q29. Winds are caused by the differences in

Solution

Winds are caused by the differences in the air pressure. Sun heats different parts of the Earth differently, causing pressure differences. Thus, the Sun is the driving force for most winds.

Q30. The _________ force can be applied only when with direct/indirect contact with the object.

Solution

The muscular force can be applied only when with direct/indirect contact with the object.

Q31. (a) What do you understand by the term atmospheric pressure? (b) What is the cause of atmospheric pressure?

Solution

(a) The thrust per unit area exerted by air on the surface of the earth is called atmospheric pressure. (b) It is the weight of the air (thrust), which is responsible for the atmospheric pressure.

Q32. What is gravitational force? Give two examples from your daily life.

Solution

The attraction of objects towards the earth is known as force of gravity or gravity.  Every object in the universe whether a small or large exerts a force on every other object, thus this force is known as gravitational force. For example, the force acting between any two books or between two students sitting next to each other etc.

Q33. Why the soles of the shoes have grooves?

Solution

The soles of the shoes have grooves in order to increase friction between the surface of the floor and the soles of the shoes. This prevents slipping on the floor.

Q34. A force that can cause or change the motion of an object by touching it is called ___________.

Solution

A force that can cause or change the motion of an object by touching it is called contact force.

Q35. If a force of 2N is applied over an area of 2 cm2, calculate the pressure produced.

Solution

  • Area = 2 cm2= 2/10000
  • = 0.0002 m2 We know that, Pressure
  • = Force/Area = 2N/0.0002 m2 
  • = 10000 Pa

Q36. The application of force on an object may change its 

Solution

Both, the speed and the direction of motion of the object, may change on applying force.

Q37. How the syringes are used to take blood for blood tests?

Solution

When the plunger of the syringe is withdrawn, the pressure inside the syringe decreases and the blood inside the body (which is at high pressure) moves into the syringe. Thus, syringes are used to take blood for blood tests.

Q38. Why does a ball rolling on the ground stop after some time?

Solution

The ball stops after some time due to the force of friction between the ball and the ground.

Q39. Give two examples, where force of friction is a hindrance.

Solution

1. It wears out the sole of shoes and  2. It wears out the moving parts of machinery.

Q40. Why does an object always fall downwards and not upwards?

Solution

This happens because the earth pulls all objects towards itself due to the attractive force called the force of gravity.

Q41. When a small rubber cup is pressed hard on a smooth plane surface, it sticks to it. Give reason.

Solution

The small rubber cup sticks to the surface because most the air between the cup and the surface escapes out ,hence the pressure inside decreases while the outer pressure which is more, acts on it.

Q42. When an object is subjected to an external stress (or pressure) with the aim to cause a reduction in its volume, the process involved is

Solution

When an object is subjected to an external stress (or pressure) with the aim to cause a reduction in its volume, this process involved is compression.

Q43. Make a list of at least four effects of force that can be produced, when an net force acting on an object is non-zero.

Solution

i. The force may make the object move from rest. ii. The force may change the speed of the object if it is moving. iii. The force may change the direction of motion of the object. iv. The force may bring about a change in the shape of the object

Q44. The atmospheric pressure on the earth’s surface at sea level is about one hundred thousand Pascal. If such an enormous amount of pressure is acting on us, why we do not feel it?

Solution

This is because the pressure of the blood in our blood vessels balances out the atmospheric pressure.

Q45. The force which is responsible for changing the state of motion of an object is called _________.

Solution

The force which is responsible for changing the state of motion of an object is called friction.

Q46. Why does a balloon expand when you blow air into it? Why does it make a noise when it’s popped?

Solution

When a balloon is blown up, the air pressure inside the balloon slowly becomes greater than the air pressure outside the balloon. Since the balloon is made of rubber and is expandable, it grows larger and larger. When the balloon is popped, the air escapes instantly. The sound heard is due to the molecules of air inside the balloon coming into sudden contact with the molecules of air outside the balloon.

Q47.  In what ways atmospheric pressure is similar to liquid pressure?

Solution

Atmospheric pressure is similar to liquid pressure in the following ways: 1. Both of these pressures act in all directions. 2. Both of these pressures become less as we rise up through air or liquid. Atmospheric pressure is similar to liquid pressure in the following ways: 1. Both these pressures act in all directions. 2. Both these pressures become less as we rise up through the liquid or air.

Q48. Why the wall of a dam is made stronger and thicker at the bottom than at the top?

Solution

The wall of a dam is made stronger and thicker at the bottom than at the top so as to withstand high sideways pressure exerted by deep water stored in the reservoir of the dam.