1. Laws of Motion

9th science Laws of motion

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Q.1.  Fill in the blank and rewrite the completed statements                                                            23

1 .is the displacement that occurs in unit time.

Ans Velocity is the displacement that occurs in unit time.

2.The distance travelled by an object in a particular direction in unit time is called …………. .

Ans The distance travelled by an object in a particular direction in unit time is called velocity.

3.If an object covers unequal distance in equal time intervals, it is said to be moving with………………………….. speed.

Ans If an object covers unequal distance in equal time intervals, it is said to be moving with non-uniform speed.

4.The product of mass and velocity is called …………. .

Ans The product of mass and velocity is called momentum.

5.When the velocity of an object increase, the acceleration is …………. .

Ans When the velocity of an object increase, the acceleration is Positive.

6.When a bullet is fired from the gun, the gun moves in backward direction. This motion is called as …………. .

Ans When a bullet is fired from the gun, the gun moves in backward direction. This motion is called as recoil.

7.When the velocity of an object decrease, the acceleration is …………. .

Ans When the velocity of an object decrease, the acceleration is negative.

8.The…………………….. force causes the change in the state of an object at rest or in uniform motion.

Ans The unbalanced force causes the change in the state of an object at rest or in uniform motion.

9.The third equation of motion gives the relation between displacement and …………. .

Ans The third equation of motion gives the relation between displacement and velocity.

10.A body is said to be in……………………. if it changes its position with respect to its surrounding.

Ans A body is said to be in motion if it changes its position with respect to its surrounding.

11.The first equation of motion gives the relation between………………………. and time.

Ans The first equation of motion gives the relation between Velocity and time.

12……………. is the length of the actual path covered by an object in motion while going from one point to another.

Ans Distance is the length of the actual path covered by an object in motion while going from one point to another.

13.When an object moves with constant speed along a circular path, the motion is called…………………………. motion.

Ans When an object moves with constant speed along a circular path, the motion is called uniform circular motion.

14.………….is a relative concept.

Ans Motion is a relative concept.

15.Newton’s first law of motion explains the phenomenon of …………. .

Ans Newton’s first law of motion explains the phenomenon of Inertia.

16.The distance covered by an object in unit time is called ……………. .

Ans The distance covered by an object in unit time is called speed.

17.In CGS system, the unit of force is …………. .

Ans In CGS system, the unit of force is dyne.

 18.The second equation of motion gives the relation between………………………….. and time.

Ans The second equation of motion gives the relation between Displacement and time.

19.The S.I. unit of speed is ………….

Ans The S.I. unit of speed is m/s.

20.A body is said to be at………………………. if it does not change its position with respect to its surrounding.

Ans A body is said to be at rest if it does not change its position with respect to its surrounding.

21.Motion of an object was studied by …………. .

Ans Motion of an object was studied by Sir Isaac Newton.

 22.The rate of change of velocity is called Acceleration.

Ans The rate of change of velocity is called acceleration.

23.If an object covers equal distance in equal time intervals, it is said to be moving with………………………… speed.

Ans If an object covers equal distance in equal time intervals, it is said to be moving with uniform speed.

Q.2. Find the odd one out                3

1.Force, Momentum, Acceleration, Mass.

Ans Mass: It is scalar quantity whereas remaining are vector quantities.

2.Motion of vehicles on a crowded street, a man going for a stroll on a beach, soldiers marching, motion of fishes in water.

Ans Soldiers marching This is an example of uniform motion whereas the rest are examples of non-uniform motion.

3.newton, joule, kg m/s2, dyne

Ans joule: It is a unit of energy whereas remaining are units of force.

Q.3. Find co-related terms               8

1    1 m/s2 : 102 cm/s2 :: 1 N : ………..

Ans 1 m/s2 : 102 cm/s2 :: 1 N : 105 dynes.

1 N = 1 kg × 1 m/s2 = 103 g × 102 cm/s2

= 105 g cm/s2

= 105 dynes

2. Velocity : m/s ::………………………… m/s2

Ans Velocity : m/s :: Acceleration : m/s2

3.Tendency of a body to resist change in a state of rest or state of motion : Inertia :: Product of mass and velocity of an object :

Ans Tendency of a body to resist change in a state of rest or state of motion : Inertia :: Product of mass and velocity of an object : Momentum.

Tendency of a body to resist change in a state of rest or state of motion is termed as inertia, similarly product of mass and velocity of an object is termed as momentum.

4. S.I. unit of momentum: Kg.m/s2:: C.G.S unit of momentum: ……………

Ans S.I. unit of momentum: Kg.m/s2:: C.G.S unit of momentum: g.cm/s2

5. Speed : Distance :: Velocity: ……………

Ans: Speed : Distance :: Velocity: Displacement

 6. Speed of light : 3 x 108m/s :: Speed of sound : ……………

Ans Speed of light : 3 x 108m/s :: Speed of sound : 7.343.2m/s1 7.  kg × 1 m/s2 : 1 N :: 1 g × 1 cm/s2 :          

Ans 1 kg × 1 m/s2 : 1 N :: 1 g × 1 cm/s2 : 1 dyne.

Product of 1 kg and 1 m/s2 is equivalent to 1 N, similarly product of 1 g and 1 cm/s2 is equivalent to 1 dyne.

4. S.I. unit of force:………………… : : C.G.S unit of force: dyne

Ans S.I. unit of force: newton : : C.G.S unit of force: dyne

Q.4. Match the pair              3

1.

Column “A” Column “B”
a. Describes the relationship between the forces on two interacting object
i. Newton’s first law of motion.
ii. Newton’s second law of motion
b. Also called the law of inertia
iii. Newton’s third law of motion c. Gives the idea of effects of force

 

Ans:

i. Newton’s first law of motion Also called the law of inertia
ii. Newton’s second law of motion
Gives the idea of effects of force
iii. Newton’s third law of motion Describes the relationship between the forces on two interacting object

 

Ans

Column “A” Column “B”
i. Newton’s first law of motion a. Motion of rocket
ii. Newton’s second law of motion b. Only the carom coin at the bottom of a pile moves on been hit by the striker
iii. Newton’s third law of motion c. In a high jump athletic event, the athletes are made to fall on a sand bed

 

2.

i. Newton’s first law of motion Only the carom coin at the bottom of a pile moves on been hit by the striker
ii. Newton’s second law of motion In a high jump athletic event, the athletes are made to fall on a sand bed
iii. Newton’s third law of motion
Motion of rocket

 

Ans:

Column “A” Column “B”
i. Inertia a. Body at rest
ii. Rate of change of momentum b. Newton’s first law
c. Newton’s second law

 

3.

d. Mass x Acceleration
i. Inertia Newton’s first law
ii. Rate of change of momentum Newton’s second law

 

Q. 5. State True or False 12

1. Action and reaction forces act simultaneously.

Ans Action and reaction forces act simultaneously. – True

 2. In S.I. system, the unit of force is dyne.

Ans False – In S.I. system, the unit of force is newton.

3.During collision the total momentum remains constant.

Ans During collision the total momentum remains constant. – True

4.. The distance and displacement are equal only if motion is along a straight line.

Ans The distance and displacement are equal only if motion is along a straight line. – True

5. The balanced force causes a change in the state of rest of an object.

Ans False – The unbalanced force causes a change in the state of rest of an object.

6.A body moving with a uniform velocity is said to have uniform acceleration.

Ans False – In uniform acceleration, velocity changes by equal amounts in equal time interval.

7. Distance is vector quantity.

Ans False – Displacement is a vector quantity as it has both magnitude and direction.

8.The inertia of the body is measured in terms of mass.

Ans The inertia of the body is measured in terms of mass. – True

9. Positive acceleration is called deceleration.

Ans False – negative acceleration is called deceleration.

10 .In uniform circular motion, the direction of motion is tangential.

Ans In uniform circular motion, the direction of motion is tangential. – True

 11. An object covers unequal distance in equal time intervals then it is moving with non-uniform speed.

Ans An object covers unequal distance in equal time intervals then it is moving with non-uniform speed. – True

 12. The velocity of a body is given by the distance covered by it in unit time in a given direction.

Ans The velocity of a body is given by the distance covered by it in unit time in a given direction. – True

 

Q.6. Name the following                          12

1.The scientist who summarized motion in a set of equations of motion.

Ans Sir Isaac Newton

2. When an object comes to rest at the end of its motion, what is its final velocity?

Ans Final velocity (v)=0

3. Negative acceleration is also called.

Ans Deceleration

4. The motion that covers unequal distance in equal interval of time.

Ans Non-uniform motion

5. S.I. unit of velocity.

Ans m/s

6. S.I. unit of momentum

Ans kg m/s

7. The motion that covers equal distance in equal interval of time.

Ans Uniform motion

8. S.I. unit of acceleration.

Ans m/s2

9. What is the backward motion of the gun called?

Ans recoil

10. Motion of an object along a circular path with uniform speed.

Ans Uniform circular motion

11. When an object is at rest in the beginning of its motion, what is its initial velocity?

Ans Initial velocity (u)= 0

12. What are the two types of acceleration for an object in motion?

Ans Uniform acceleration and Non-uniform acceleration.

Q. 7. Multiple Choice Questions                           10

  1. A car is moving with a velocity of 50km/hr for 5 hours, is an example of …………….

a. zero acceleration b. positive acceleration

negative acceleration d. retardation

Ans Option a.

 

  1. v 2 = u2 + 2as is the relation between …………….
  2. speed and velocity b. displacement and velocity
  3. displacement and time d. velocity and time

Ans Option b.

 

  1. The force necessary to cause an acceleration of 1m/s2 in an object of mass 1kg is called …………… .
  2. 1 dyne b. 1 newton c. acceleration             d. inertia

 

Ans Option b.

 

  1. An object continues to remain at rest or in a state of uniform motion along a straight line unless an ……………

acts on it.

  1. external balanced force b. external unbalanced force
  2. internal balanced force d. internal unbalanced force

Ans Option b.

 

  1. ……….is an example of negative acceleration.
  2. A coin thrown vertically upwards b. A coin falls freely towards the earth
  3. A train starting from the station d. An object is speeding up.

Ans Option a.

 

  1. If the velocity changes by equal amounts in equal time intervals, the object is said to have …………… .
  2. uniform velocity b. non-uniform velocity
  3. non-uniform motion d. uniform acceleration.

 

Ans Option d.

 

  1. The displacement that occurs in unit time is called ……………

A . direction           b. velocity             c. peed   d. acceleration

 

Ans Option b.

 

  1. Even if the displacement of an object is zero, the actual distance traveled by the object …………… .
  2. will be constant b. will be zero
  3. may not be zero d. will be negative

 

Ans Option c.

 

  1. The velocity of a body changes when …………… .
  2. Speed changes but direction is constant
  3. direction changes but speed is constant
  4. Speed and direction changes
  5. All of the three

Ans Option d.

 

  1. v = u + at is the relation between …………….
  2. speed and velocity b. displacement and velocity
  3. displacement and time d. velocity and time

Ans Option d.

 

P H Dhakne
http://phdsciencegyan.com

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