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Selina solutions for Class 8 Physics chapter 3 - Force and Pressure

Selina Concise Physics - Middle School for Class 8 (2018-19 Session)

Selina Selina Concise Physics - Middle School Class 8 (2018-19 Session) Chapter 3: Force and Pressure

Chapter 3: Force and Pressure solutions [Page 0]

True or False

Water in a lake exerts pressure only at its bottom.

• True

• False

True and False

A force always produces both the linear and turning motions.

True and False

Moment of force = force × perpendicular distance of force –  from the pivoted point.

True and False

Less force is needed when applied at a farther distance from the pivoted point.

True and False

For a given thrust, pressure is more on a surface of large j area.

True and False

The pressure on a surface increases with an increase in the thrust on the surface.

True and False

A man exerts same pressure on the ground whether he is standing or he is lying.

True and False

It is easier to hammer a blunt nail into a piece of wood than a sharply pointed nail.

True and False

The S.I. unit of pressure is pascal.

True and False

The S.I. unit of force is kgf.

True and False

A liquid exerts pressure in all directions.

True and False

Gases exert pressure in all directions.

True and False

The atmospheric pressure is nearly 105 Pa.

True and False

Higher we go, greater is the air pressure.

Fill in the blank

1 kgf = .............. (nearly).

Fill in the blank

Moment of force =...............  × distance of force from the point of turning.

Fill in the blank

In a door, handle is provided  ......... from the hinges.

Fill in blank

The unit of thrust is  ..........

Fill in blank

hrust is the ............ force acting on a surface.

Fill in blank

Pressure is the thrust acting on a surface of ........... area.

Fill in blank

The unit of pressure is  ........ .

Fill in blank

Pressure is reduced if.................... increases.

Fill in blank

Pressure in a liquid ................with the depth.

Fill in blank

The atmospheric pressure on earth surface is nearly .............. .

Match the column

 Column A Column B (a) Camel (1) broad and deep foundation (b) Truck (2) broad feet (c) Knife (3) six or eight tyres (d) High building (4) sharp cutting edge (e) Thrust (5) atm (f) Moment of force (6) N (g) Atmospheric pressure (7) N m

Select the correct alternative

SI. unit of moment of force is

1. N
2.  N cm
3.  kgfm
4.  N m

Select the correct alternative

To obtain a given moment of force for turning a body, the force needed can be decreased by

1. applying the force at the pivoted point
2.  applying the force very close to the pivoted point
3.  applying the force farthest from the pivoted point
4.  none of the above

Select the correct alternative

The unit of thrust is

1. kgf
2.  kg
3.  g
4. m s-1

Select the correct alternative

The unit of pressure is

1.  N × m
2.  kgf
3.  N m-2
4.  kgf m2

Select the correct alternative

The pressure and thrust are related as

1. Pressure = Thrust
2.  Pressure = Thrust x Area
3. Pressure = Thrust / Area,
4.  Pressure = Area / Thrust

Select the correct alternative

A body weighing 5 kgf, placed on a surface of area 0.1 m2, exerts a thrust on the surface equal to

1.  50 kgf
2.  5 kgf
3.  50 kgf  m-2
4.  5 kgf  m-2

Select the correct alternative

A body weighing 5 kgf, placed on a surface of area 0.1 m2, exerts a pressure on the surface equal to

1. 50 kgf
2.  5 kgf
3.  50 kgf m-2
4.  5 kgf m-2

Select the correct alternative

The feet of lizards act like

4.  none of the above

Select the correct alternative

Pressure exerted by a liquid is due to its

1.  weight
2.  mass
3. volume
4.  area

Select the correct alternative

Pressure inside a liquid increases with :

1.  increase in depth
2.  decrease in depth
3.  decrease in density
4.  none of the above

Select the correct alternative

The atmospheric pressure at sea level is nearly

1. 10 Pa
2.  100,000 Pa
3.  100 Pa
4.  10,000 Pa

Select the correct alternative

Nose bleeding may occur at a high altitude because

1.  the atmospheric pressure decreases
2.  the oxygen content of atmosphere decreases
3.  the atmospheric pressure increasess
4.  there are strong air currents at the high altitude

Chapter 3: Force and Pressure solutions [Page 0]

Define force. State its S.I. unit.

State two effects of a force when applied on a body.

A spanner of length 10 cm is used to open a nut by applying a minimum force of 5.0 N. Calculate the moment of force required.

How does the effect of force differ when it is applied on a rigid body?

How does the effect of force differ when it is applied on a non-rigid body?

State the effect of force F in of the following diagram. State the effect of force F in  of the following diagram. Define the term moment of force.

State the S.I. unit of moment of force.

State two factors on which affect moment of force.

In Fig. a force F is applied in a direction passing through the pivoted point O of the body. Will the body rotate ? Give reason to support your answer. Write the expression for the moment of force about a given axis of rotation.

State one way to decrease the moment of a given force about a given axis of rotation.

State one way to obtain greater moment of a given force about a given axis of rotation.

What do you mean by the clockwise and anti-clockwise moment of force ?

Explain the following:
The spanner (or wrench) has a long handle.

Explain the following:

The steering wheel of a vehicle is of large diameter.

The hand flour grinder is provided with a handle near the rim.

Explain the following:

It is easier to open the door by pushing it at its free end.

A potter turns his wheel by applying a force through the stick near the rim of wheel.

What is thrust ?

State the unit of thrust

On what factors does the effect of thrust on a surface depend?

Define the term ‘pressure’ and state its unit.

How is the thrust related to pressure ?

Name two factors on which the pressure on a surface depends.

When does a man exert more pressure on the floor : while standing or while walking ?

Why do camels or elephants have broad feet ?

A sharp pin works better than a blunt pin. Explain the reason.

Why is the bottom part of the foundation of a building made wider ?

It is easier to cut with a sharp knife than with a blunt one. Explain.

A gum bottle rests on its base. If it is placed upside down, how does the thrust .

A gum bottle rests on its base. If it is placed upside down, how does the  pressure change ?

Explain the following:

Sleepers are used below the rails.

Explain the following:
A tall building has wide foundations.

Describe an experiment to show that a liquid exerts pressure at the bottom of the container in which it is kept.

Describe a suitable experiment to demonstrate that a liquid exerts pressure sideways also ?

Describe a simple experiment to show that at a given depth, a liquid exerts same pressure in all directions.

State two factors on which the pressure at a point in a liquid depends.

Describe an experiment to show that the liquid pressure at a point increases with the increase in height of the liquid column above that point.

Which fact about liquid pressure does the diagram in fig. illustrate.

Describe an experiment to show that liquid pressure depends on the density of liquid.

A dam has broader walls at the bottom than at the top. Give a reason.

What do you mean by atmospheric pressure ?

Write the numerical value of the atmospheric pressure on the earth surface in pascal.

We do not feel uneasy even under the enormous atmospheric pressure. Give a reason.

Describe a simple experiment to illustrate that air exerts pressure.

Describe the crushing tin can experiment. What do you conclude from this experiment ?

Give reason for the following :
Water does not run out of a dropper unless its rubber bulb is pressed.

Give reason for the following :
Two holes are made in a sealed oil tin to take out oil from it.

How does the atmospheric pressure change with altitude?

Give reason for the following :
A balloon collapses when air is removed from it.

Chapter 3: Force and Pressure solutions [Page 0]

Find the moment of force of 20 N about an axis of rotation at distance 0.5 m from the force.

The moment of a force of 25 N about a point is 2.5 N m. Find the perpendicular distance of force from that point

A spanner of length 10 cm is used to open a nut by applying a minimum force of 5.0 N. Calculate the moment of force required.

A wheel of diameter 2 in can be rotated about an axis passing through its centre by a moment of force equal to 2e0 N m. What minimum force must be applied on its rim?

A normal force of 200 N acts on an area of 0.02 m2. Find the pressure in pascal.

Find the thrust required to exert a pressure of 50000 pascals on an area of 0.05 m2 ?

Find the area of a body which experiences a pressure of50000 Pa by a thrust of 100 N ?

Calculate the pressure in pascal exerted by a force of 300 N acting normally on an area of 30 cm2.

How much thrust will be required to exert a pressure of 20,000 Pa on an area of 1 cm2.

The base of a container measures 15 cm × 20 cm. It is placed on a table top. If the weight of the container is 60 N, what is the pressure exerted by the container on the table top ?

Calculate the pressure exerted on a surface of 0.5 m2 by a thrust of 100 kgf.

A boy weighing 60 kgf stands oixplatform of dimensions 2.5 cm x 0.5 cm. What pressure in pascal does he exert ?

Figure shows a brick of weight 2 kgf and dimensions 20 cm x 10 cm × 5 cm placed in three different positions on the ground. Find the pressure exerted by the brick in each case. Chapter 3: Force and Pressure

Selina Selina Concise Physics - Middle School Class 8 (2018-19 Session) Selina solutions for Class 8 Physics chapter 3 - Force and Pressure

Selina solutions for Class 8 Physics chapter 3 (Force and Pressure) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CISCE Selina Concise Physics - Middle School for Class 8 (2018-19 Session) solutions in a manner that help students grasp basic concepts better and faster.

Further, we at Shaalaa.com are providing such solutions so that students can prepare for written exams. Selina textbook solutions can be a core help for self-study and acts as a perfect self-help guidance for students.

Concepts covered in Class 8 Physics chapter 3 Force and Pressure are Turning Effect of Force (Moment of Force), Concept of Pressure, Pressure - Unit, Pressure - Calculation of Pressure in Simple Cases, Pressure Exerted by Liquids and Gases, Atmospheric Pressure.

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