General Science Solutions Solutions for Class 8 Science Chapter 3 Force And Pressure are provided here with simple step-by-step explanations. These solutions for Force And Pressure are extremely popular among Class 8 students for Science Force And Pressure Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the General Science Solutions Book of Class 8 Science Chapter 3 are provided here for you for free. You will also love the ad-free experience on Meritnationâ€™s General Science Solutions Solutions. All General Science Solutions Solutions for class Class 8 Science are prepared by experts and are 100% accurate.

#### Page No 22:

#### Question 1:

Write the word in the blank space.

A. The SI unit of force is_________ (Dyne, Newton, Joule)

B. The air pressure on our body is equal to __________ pressure (Atmospheric, sea bottom, space)

C. For a given object, the buoyant force in liquids of different ________ is__________ (the same, density, different, area)

D. The SI unit of pressure is_______ (N/m^{3 }, N/m^{2}, kg/m^{2}, pa/m^{2})

#### Answer:

A. The SI unit of force is __Newton__.

B. The air pressure on our body is equal to __atmospheric__ pressure.

C. For a given object, the buoyant force in liquids of different __density__ is __different__.

D. The SI unit of pressure is __N/m__^{2}.

#### Page No 22:

#### Question 2:

Make a match

A group | B group |

1. Fluid | a. Higher pressure |

2. Blunt knife | b. Atmospheric pressure |

3. sharp needle | c. Specific gravity |

4.Relative density | d. Lower pressure |

5. Hecto pascal | e. Same pressure in all directions |

#### Answer:

A group |
B group |

1. Fluid | e. Same pressure in all directions |

2. Blunt knife | d. Lower pressure |

3. sharp needle | a. Higher pressure |

4. Relative density | c. Specific gravity |

5. Hecto pascal | b. Atmospheric pressure |

#### Page No 22:

#### Question 3:

Answer the following questions in brief.

A. A plastic cube is released in water. Will it sink of come to the surface of watet?

B. Why do the load carrying heavy vehicles have large number of wheels?

C. How much pressure do we carry on our heads? why don't we feel it?

#### Answer:

(a) The plastic cube is going to float on the surface of water as its density is less than that of water.

(b) We know, $\mathrm{Pressure}=\frac{\mathrm{Force}}{\mathrm{Area}}$

So, greater the area of contact between two surfaces, lesser will be the pressure. So, the load carrying heavy vehicles have large number of wheels so that the pressure on the road is reduced due to larger contact area. Also, using large number of wheels ensures that the force due to the load is shared among the tyres and no single tyre is under stress.

(c) We carry atmospheric pressure of about 10^{5} Pa on our heads. We don't feel it because this atmospheric pressure is balanced by the pressure created by the air and blood inside our body.

#### Page No 22:

#### Question 4:

Why does it happen?

A. A ship dips to a larger depth in fresh water as compared to marine water.

B. Fruits can easily be cut with a sharp knife.

C. The wall of a dam is broad at its base.

D. If a stationary bus suddenly speeds up, passengers are thrown in the backward direction.

#### Answer:

A. The density of marine water is more than the fresh water due to which the buoyant force on the ship in marine water is more than the fresh water. Hence, the ship dips to a larger depth in fresh water as compared to marine water.

B. Since the sharp edged knife makes lesser contact with the fruits to be cut, thus the pressure exerted by it on the fruit is very large. Because of this large pressure, fruits are easily cut with a sharp knife.

C. We know pressure of liquid increases with depth. So, the wall of a dam is made broader at its base so that it is able to withstand the heavy pressure exerted by the river water.

D. If a stationary bus suddenly speeds up, passengers are thrown in the backward direction. This is because initially the whole body of a passenger inside the bus was in the state of rest. But, when the bus suddenly starts or speeds up, the lower half of the passenger's body comes in motion in the forward direction but the upper half still remains at rest due to inertia of rest. Hence, the passengers are thrown backward when a stationary bus suddenly speeds up.

#### Page No 22:

#### Question 5:

Complete the following tables.

Mass(Kg) | Volume (m^{3}) |
Density(kg/m^{3}) |

350 | 175 | - |

- | 190 | 4 |

Density of Metal (kg/m^{3}) |
Density of water (kg/m^{3}) |
Relative Density |

10^{3} |
5 | |

8.5$\times $10^{3} |
10^{3} |
- |

weight(N) | Area (m^{2}) |
Pressure(Nm^{−2}) |

- | 0.04 | 20,000 |

1500 | 500 | - |

#### Answer:

We know, $\mathrm{Density}=\frac{\mathrm{Mass}}{\mathrm{Volume}}$

So, using above formula, we can find one quantity if other two quantities are given.

Mass (kg) | Volume (m^{3}) |
Density (kg/m^{3}) |

350 | 175 | 2 |

760 | 190 | 4 |

We know, $\mathrm{Relative}\mathrm{density}\mathrm{of}\mathrm{substance}=\frac{\mathrm{Density}\mathrm{of}\mathrm{substance}}{\mathrm{Density}\mathrm{of}\mathrm{water}}$

So, using above formula, we can find one quantity if other two quantities are given.

Density of Metal (kg/m^{3}) |
Density of water (kg/m^{3}) |
Relative Density |

5$\times $10^{3} |
10^{3} |
5 |

8.5$\times $10^{3} |
10^{3} |
8.5 |

We know, $\mathrm{Pressure}=\frac{\mathrm{Force}}{\mathrm{Area}}$

So, using above formula, we can find one quantity if other two quantities are given.

Weight (N) | Area (m^{2}) |
Pressure (N m^{−2}) |

800 | 0.04 | 20,000 |

1500 | 500 | 3 |

#### Page No 22:

#### Question 6:

The density of a metal is $10.8\times {10}^{3}\mathrm{kg}/{\mathrm{m}}^{3}$. Find the relative density of the metal.

#### Answer:

Given:

Density of metal = $10.8\times {10}^{3}\mathrm{kg}/{\mathrm{m}}^{3}$

We know, density of water = 1000 kg/m^{3}

$\mathrm{Relative}\mathrm{density}\mathrm{of}\mathrm{substance}=\frac{\mathrm{Density}\mathrm{of}\mathrm{substance}}{\mathrm{Density}\mathrm{of}\mathrm{water}}$

$\mathrm{Relative}\mathrm{density}\mathrm{of}\mathrm{substance}=\frac{10.8\times {10}^{3}}{1000}=10.8$

#### Page No 22:

#### Question 7:

Volume of an object is 20 cm^{3} and the mass in 50 g. Density of water is 1 g cm^{$-$3}. Will the object float on water or sink in water?

#### Answer:

Given:

Volume of object = 20 cm^{3}

Mass of object = 50 g

Density of object = $\frac{\mathrm{Mass}\mathrm{of}\mathrm{object}}{\mathrm{Volume}\mathrm{of}\mathrm{object}}=\frac{50}{20}=2.5\mathrm{g}/{\mathrm{cm}}^{3}$

Now, we know density of water = 1 g/cm^{3}

Since, density of object > density of water, therefore the object is going to sink in water.

#### Page No 22:

#### Question 8:

The volume of a plastic covered sealed box is 350 cm^{3} and the box has a mass 500 g. Will the box float on water or sink in water? what will be the mass of water displaced by the box?

#### Answer:

Given:

Volume of box = 350 cm^{3}

Mass of box = 500 g

Density of object = $\frac{\mathrm{Mass}\mathrm{of}\mathrm{object}}{\mathrm{Volume}\mathrm{of}\mathrm{object}}=\frac{500}{350}=1.43\mathrm{g}/{\mathrm{cm}}^{3}$

Now, we know density of water = 1 g/cm^{3}

Since, density of box > density of water, therefore the object is going to sink in water.

Now, volume of liquid displaced = Volume of the object = 350 cm^{3
$\Rightarrow \frac{\mathrm{Mass}\mathrm{of}\mathrm{liquid}\mathrm{displaced}}{\mathrm{Density}\mathrm{of}\mathrm{liquid}\mathrm{displaced}}=350{\mathrm{cm}}^{3}\phantom{\rule{0ex}{0ex}}\Rightarrow \mathrm{Mass}\mathrm{of}\mathrm{liquid}=350\times 1=350\mathrm{g}$ }

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