# CBSE Class 9 - Physics - Work (Questions and Answers)

**Q1: 2 Newton-metre is how many joules?**

Answer: ∵ 1 Nm = 1J ∴ 2Nm = 2J

**Q2: In the CGS system, what is the unit for Work?**

Answer: erg

Showing posts with label **class9-physics**. Show all posts

Showing posts with label **class9-physics**. Show all posts

**Q1: 2 Newton-metre is how many joules?**

Answer: ∵ 1 Nm = 1J ∴ 2Nm = 2J

**Q2: In the CGS system, what is the unit for Work?**

Answer: erg

**Q1. Rusting of an article made up of iron is called**

(a) corrosion and it is a physical as well as chemical change

(b) dissolution and it is a physical change

(c) corrosion and it is a chemical change

(d) dissolution and it is a chemical change

No. | Discovery | Scientist | Year |
---|---|---|---|

1. | Proton | Rutherford | 1919 |

2. | Neutron | James Chadwick | 1932 |

3. | Atom | John Dalton | 1808 |

4. | Atomic Structure | Neil Bohr & Rutherford | 1913 |

5. | Radioactivity | Henry Becquerel | 1896 |

6. | Radium | Madam Curie | 1898 |

7. | Raman Effect | CV. Raman | 1928 |

8. | X-Rays | Roentgen | 1895 |

9. | Photoelectric effect | Albert Einstein | 1905 |

10. | Periodic table | Mendeleev | 1888 |

11. | Nuclear Reactor | Anrico Fermi | 1942 |

12. | Wireless Telegram | Marconi | 1901 |

13. | Dynamite | Alfred Nobel | 1867 |

Class 9 - Physics

1. Energy is the __________ to do work. Its S.I. unit is ________.

2. Work is force multiplied by ___________ in the direction of force.

3. If the angle between force and the displacement caused is acute then work is said to be ________.

4. If the angle between force and the displacement caused is obtuse, the work is said to be _______.

5. One joule of work is said to be done when a force of ______ displaces a body through a distance of ________ in its own direction.

1) Find the total thrust acting on the bottom surface of a tank 4m long, 2m broad and 2m deep when fully filled with water. The density of water= 10³ kg/m³.

2) The gravitational force between two objects is 100N. How should the distance between the objects be changed so that force between them becomes 50N?

3) If the distance between two masses be increased by a factor of 6, by what factor would the mass of one of them have to be altered to maintain the same gravitational force? Would this be an increase or decrease in the mass?

4) The value of ‘g’ on earth’s surface is 9.8 m/s². Suppose the earth suddenly shrinks to one-third of its present size without losing any mass. What is the value of ‘g’ on the surface of shrunk earth?

5) Two bodies of mass 1kg and 100kg respectively are dropped simultaneously from same height 4.9m in a vacuum. Calculate and compare their final velocities just before hitting the ground and the time interval in which they will hit the ground.

6) The ratio of gravitational force on Neptune to the gravitational force on earth is 9:8. Ramesh weighs 792N on earth. Calculate his weight on Neptune.

Answer: Yes an object can have zero displacements even though it has moved through a distance. It happens when the object moves back to its original position i.e. final position coincides with the starting position.

Example: Suppose an object travels from O to C and then comes back to its original position O.

Total distance traveled = actual path covered = OC + CO = 25 + 25 = 50m

Total displacement = shortest distance between final position and initial position = 0m

Answer: A body is said to be at rest if it does not change its position with respect to a fixed point in its surroundings.

Answer: No these terms rest and motion are relative. For example, a person inside a car, carrying a ball in his hand will see the ball is at rest. While for another person, outside the car will see the ball is also moving.

Answer:

**Scalar Quantities**: Quantities that require magnitudes only to specify them are called scalar quantities or scalars. Mass, length, time, temperature, angle, area, speed, distance, volume and density are examples of scalar quantities.**Vector Quantities**: Quantities that require both magnitudes and direction to specify them are called vector quantities or vectors. Displacement, velocity, force, momentum, weight etc. are examples of vectors.

Answer:

As shown in the figure, let us assume, that the farmer starts from A.

Given, that the length of each side = 10m

Distance covered in 1 lap = Perimeter of ABCD = 4 x 10 = 40m

Time is taken by farmer to cover 1 lap = the 40s

Speed of farmer = Distance

Distance covered by farmer in 2min 20 secs = Speed x Time = 1 x 140s = 140m

Number of laps covered = 140 ÷ 40 = 3.5 laps.

⇒ After the 140s, the farmer will be at position C (i.e. 3 and ½ laps).

Displacement = AC = (AB

= (100+100)

Question: Can you find out displacement, if the farmer starts from the mid-point of AB?

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