Class 9th Physics Unit 3 Dynamics

physics 9th notes Chapter No 3

1. The weight of a body of mass 10 kg on earth will:

 
 
 
 

2. First law of motion is also known as law of

 
 
 
 

3. Value of coefficient of static friction is usually ______ than coefficient of kinetic friction:

 
 
 
 

4. Sliding friction is commonly converted into rolling friction by the use of:

 
 
 
 

5. 1 N =

 
 
 
 

6. The maximum value of static friction is known as —– friction:

 
 
 
 

7. Quantity of matter in a body:

 
 
 
 

8. The force which resists the motion of one surface on another surface is known as:

 
 
 
 

9. When a force is applied on the body, _______ is produced in the body:

 
 
 
 

10. Mass is a quantity:

 
 
 
 

11. Frictional forces follow which law of motion?

 
 
 
 

12. Isaac Newton described the laws of motion in his famous book:

 
 
 
 

13. When a block is hanging with the help of a rope then weight of the body is balanced by:

 
 
 
 

14. In rolling friction surfaces have less:

 
 
 
 

15. Law of inertia is actually the ______ law of motion:

 
 
 
 

16. When an object is in motion then the force of friction is known as ______ friction:

 
 
 
 

17. When object is at rest, the force of friction is known as:

 
 
 
 

18. If centripetal force acting on a body is doubled then its velocity will become:     

 
 
 
 

19. The value of coefficient of friction between tyre and dry road is:

 
 
 
 

20. The tension produced when one body moves vertically and the other moves horizontally is as compared to the tension produced when both bodies move vertically:

 
 
 
 

21. Rate of change of momentum is equal to:

 
 
 
 

22. When air is released from an inflated balloon, it shoots off is an example of:

 
 
 
 

23. Friction of liquids is _____ than friction of solids:

 
 
 
 

24. Static friction is:

 
 
 
 

25. Momentum of a moving body depends upon its:

 
 
 
 

26. Walking on road is an example of ______ law of motion:

 
 
 
 

27. When a block is lying on a smooth surface, its weight is balanced by:

 
 
 
 

28. The laws of motion established the relationship between motion and:

 
 
 
 

29. Kgms⁻¹ —

 
 
 
 

30. _______ of a body remains same everywhere:

 
 
 
 

31. _______of a body is the direct measure of inertia:

 
 
 
 

32. _______ is the agency which changes or tends to change the state of rest or of uniform motion of a body:

 
 
 
 

33. A spider web remains intact due to:

 
 
 
 

34. Friction in the human joints is much reduced due to the presence of:

 
 
 
 

35. Which of the following material lowers friction when pushed between metal plates? 

 
 
 
 

36. If mass of the body is doubled while keeping the force constant, then acceleration will be:

 
 
 
 

37. The acceleration produced in a moving body is always in the direction of applied:

 
 
 
 

38. Weight is a quantity:

 
 
 
 

39. SI unit of Momentum is:

 
 
 
 

40. The rolling friction is about_____–times smaller than sliding friction:

 
 
 
 

41. Mass of the body is measured by:

 
 
 
 

42. Does not remain same everywhere:

 
 
 
 

43. Weight of the body is measured by:

 
 
 
 

44. The ______ of a body always acting towards the center of the earth:

 
 
 
 

45. The value of coefficient of friction between wood and concrete is :

 
 
 
 

46. The front sides of high speed vehicles, aero planes and ships are shaped wedge like to reduce:

 
 
 
 

47. Coefficient of friction does not depend upon the ____ between two surfaces:

 
 
 
 

48. Rolling friction is ______ than Sliding friction:

 
 
 
 

49. There are _____ cases of motion of the body hanging with the help of rope:

 
 
 
 

50. The value of coefficient of friction between iron and iron is:

 
 
 
 

51. In circular motion, the motion of every particle of body is:                                

 
 
 
 

52. If the velocity of a moving body in a circle is doubled, then its centripetal force is  

 
 
 
 

53. The force which compels a body to move in circle is:

 
 
 
 

54. Which of the following is the unit of momentum?

 
 
 
 

55. The value of coefficient of friction between tyre and wet road is:

 
 
 
 

56. The characteristic of a body due to which it tends to retain its state of rest or of uniform motion is known as:

 
 
 
 

57. The value of coefficient of friction between wood and wood is :

 
 
 
 

58. Remains same everywhere:

 
 
 
 

59. _______ of a body does not remain same everywhere:

 
 
 
 

60. The coefficient of friction has unit:

 
 
 
 

61. Static friction is _____ than kinetic friction:

 
 
 
 

62. Action and reaction are equal in magnitude but opposite in direction is known as:

 
 
 
 

63. When a force of 8 newton is applied on a body of mass 2 kg, then the acceleration produced will be:

 
 
 
 

64. Direction of the rate of change of momentum is in the direction of: 

 
 
 
 

65. Motion of the rocket is an example of:

 
 
 
 

66. Always acting towards the center of the earth:

 
 
 
 

67. The Force with which earth attracts a body towards its centre is known as:

 
 
 
 

68. The value of weight of a body of constant mass depends on:

 
 
 
 

69. The centripetal acceleration is always along :       

 
 
 
 

70. SI unit of force is:

 
 
 
 

71. Product of mass and velocity is known as:

 
 
 
 

72. The unit of coefficient of friction is:

 
 
 
 

73. Quantity of motion in a body is known as:

 
 
 
 

74. Unit of weight is:

 
 
 
 

75. The characteristic of a body which determines the magnitude of acceleration produced when a certain force acts upon it:

 
 
 
 

76. Laws of motion were presented by:

 
 
 
 

77. If force applied on the body is doubled while keeping the mass constant, then acceleration will be:

 
 
 
 

78. Mass of the body is measured by:

 
 
 
 

79. Value of coefficient of friction depends upon:

 
 
 
 

Short Questions

A bullet has very small inertia due to its small mass. But why does its impact is so strong when it is fired from the gun?
A horse pushes the cart. If the action and reaction are equal and opposite then how does the cart move?
Action and reaction are always equal and opposite then why they don’t cancel each other? OR Action and reaction are always equal and opposite then how does a body move?
Can a body move along a circle without the centripetal force?
Can a body move with uniform velocity in a circle? If not, why?
Define centrifuge?
Define centripetal acceleration.
Define circular motion.
Define coefficient of friction. Write its formula and unit (if any)?
Define dynamics.
Define force? Write its formula and unit.
Define friction? Write cause of friction its formula, unit and direction.
Define inertia. Explain it with examples.
Define Momentum.
Define net Force
Define SI units of force?
Define Sliding and rolling friction?
Define System and Isolated system?
Define uniform circular motion?
Demonstrate that rolling friction is less than sliding friction?
Describe coefficient of friction ( µ ) between some common materials?
Describe the situation in daily life in which friction is most desirable?
Describe the situations in which force of friction is needed.
Describe ways to reduce friction?
Differentiate between mass and weight.
Do we roll or slide eraser to remove the pencil work from our notebook?
Explain Newton’s first law of motion by a practical example of daily life?
Explain the function of cream separator.
Explain the function of washing machine (dryer).
Friction is ‘necessary evil’. Comment.
Give the microscopic concept of friction?
Have you noticed why a moving ball stops?
How can you relate a force with the change of momentum of a body?
How does oiling the moving parts of a machine lowers friction?
Identify the use of centripetal force in (i) safe driving by banking roads (ii) washing machine dryer (iii) cream separator.
If a moving body has no acceleration; does it mean that no force is acting on it?
In which case do you need smaller force and why?
Is there any reaction? If yes, then what is its direction?
Momentum of a body depends on which factors?
Moon revolves around the earth, from where it gets necessary centripetal force?
Prove that kgms⁻¹ =Ns
State Law of Conservation of Momentum.
State Newton’s Second Law of Motion in terms of Momentum.
State Newton’s Second law of motion.
State Newton’s Third law of motion.
Stretch out your palm and hold a book in it. How much force do you need to prevent the book from falling? Which is the action? Is there any reaction? If yes, then what is its direction?
Suppose you are running and want to stop at once. Surely you will have to produce negative acceleration in your speed. Can you tell from where does the necessary force come?
What is the Law of Inertia?
The first thing about a wheel is that it rolls as it moves rather than to slide. This greatly reduces friction. Why?
Under which principle rockets and jet engines works?
What are the disadvantages of friction?
What are the methods to reduce friction?
What do you know about friction?
What do you know about tension and acceleration in a string?
What do you know about the (i) tension in a string (ii)  limiting force of friction (iii) braking force (iv) skidding of vehicles (v)seatbelts (vi) banking of roads (vii)cream separator      
What do you know about the coefficient of friction?
What is action?
What is law of inertia?
What is momentum?
What is role of crumple zones in front and rare part of vehicles?
What is the centrifugal force?
What is the difference between Action and reaction
What is the difference between Mass and weight
What is the difference between sliding friction and rolling friction
What is the law of conservation of momentum?
What is the law of inertia?
What is the unit of force? Define it.
What will be the tension in a rope that is pulled from its ends by two opposite forces 100N each?
What would happen if all friction suddenly disappears?
What you know about limiting force of friction?
When a bus takes a sharp turn why do passengers fall in outward direction?
When a gun is fired, it recoils. Why?
Why a cyclist applies brakes to stop his/her bicycle?
Why are fragile objects packed in Styrofoam rings or polythene sheets with air cavities in it?
Why ball bearing or roller bearings are used to reduce friction?
Why bicycle stops when the cyclist stops peddling?
Why cyclists bend himself toward the inner side of the curved path while taking turn with high speed?
Why friction opposes motion?
Why is the law of conservation of momentum important?
Why it is dangerous to drive on a wet road?
Why it is dangerous to travel on the roof of a bus?
Why newton’s first law of motion is also known as the law of inertia?
Why outer edge of the road is kept higher than inner edge (banking of road)? Explain.
Why Rolling friction is always less than sliding friction why?
Why the impact of the loaded truck on a body coming it’s the way is very large even if the truck is moving slowly.
Why the passengers standing in a bus fall forward when the driver applies brakes suddenly?
Why the spinner of the washing machine is made to spin at a very high speed?
Write a dream during which you are driving a car and suddenly the friction disappears. What happened next…?
Write down the advantages and disadvantages of friction.
Write down the methods to reduce friction.
Write relation between Force and Momentum.
Write role of seat belts.
Write some situations where friction is desirable OR Describe two situations in which force of friction is needed.
Write some situations where friction is undesirable

Long Questions

 

Define the following terms:
(i) Inertia   (ii) Momentum    (iii) Force
(iv) Force of friction    (v) Centripetal force
A body has weight 20 N. How much force is required to move it vertically upward with an acceleration of 2 ms⁻²?
A force of 20 N moves a body with an acceleration of 2 ms⁻² . What is its mass?
Calculate the tension and acceleration in a string during motion of two bodies attached to the ends of a string that passes over a frictionless pulley such that one body moves vertically and the other moves on a smooth horizontal surface:
Calculate the tension and acceleration in the string during motion of bodies connected by the string and passing over friction pulley using the second law of motion?
Define centripetal force and centripetal acceleration and derive the mathematical
Define the centripetal force. Derive the relation of centripetal force on a body moving in a circle?
Derive Newton’s Second Law of motion with the help of momentum.
Differentiate between Mass and Weight.
Explain breaking force and skidding of vehicles?
Explain the roll of friction in Braking and explain the Skidding.
Explain the rolling friction.
Explain the tension in the string. If two bodies of masses ml and m² are hanging from
Find the acceleration produced by a force of 100 N in a mass of 50 kg.
How can you relate a force with the change of momentum of a body?
How much centripetal force is needed to make a body of mass 0.5 kg to move in a circle of radius 50 cm with a speed 3 ms⁻¹?
How much force is needed to prevent a body of mass 10 kg from falling?
How much is the force of friction between a wooden block of mass 5 kg and the horizontal marble floor? The coefficient of friction between wood and the marble is 0.6.
How much time is required to change 22 Ns momentum by a force of 20 N?
How you can prove that rate of change in momentum of a body is equal to the applied
Prove that F = ΔP/t .
Show that F = ma.
Show that Ns = Kg m/s 
Show the relationship between momentum and force?
State and Explain Newton’s First law of motion
State and Explain Newton’s Second law of motion
State and Explain Newton’s Third law of motion
State and explain the law of conservation of momentum?
The weight of a body is 147 N. What is its mass? (Take the value of g as 10 ms⁻² )
Two masses 26 kg and 24 kg are attached to the ends of a string which passes over a frictionless pulley. 26 kg is lying over a smooth horizontal table. 24 N mass is moving vertically downward. Find the tension in the string and the acceleration in the bodies.  
Two masses 52 kg and 48 kg are attached to the ends of a string that passes over a frictionless pulley. Find the tension in the string and acceleration in the bodies when both the masses are moving vertically.
What do you know about the (i) tension in a string (ii)  limiting force of friction (iii) braking force (iv) skidding of vehicles (v)seatbelts (vi) banking of roads (vii)cream separator      
What is the law of conservation of momentum?

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