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Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd

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Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd

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Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd

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Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd

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Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Why the gas
particles ejected?

6.
Law of conservation of momentum.
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Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd

7.
Law of conservation of momentum
For two or more bodies in an isolated system acting
upon each other, their total momentum remains constant unless
an external force is applied.
i.e., P initial = P final
⟹ m1u1+m2u2= m1v1+m2v2
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd

8.
Law of conservation of momentum
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Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd

9.
Law of conservation of momentum
Newton’s cradle
• Used to demonstrates the conservation of
momentum.
• Sphere at the end lifted and released
leads to pushes the last sphere upwards.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd

10.
Questions related to law of conservation of momentum
Ques1.Calculate the recoil velocity of a gun having mass
equal to 5 kg, if a bullet of 25 g acquires the velocity of 500
ms-1 after firing from the gun.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum
Solution:
Given,
Bullet;m1=25g=0.025kg, u1=0ms-1 ,v1=500ms-1 ,
Gun; m2 =5kg ,u2=0ms-1 , v2 =?
From Law of the conservation of momentum, P initial = P final
⟹ m1u1+m2u2= m1v1+m2v2

11.
Questions related to law of conservation of momentum
Ques1.Calculate the recoil velocity of a gun having mass
equal to 5 kg, if a bullet of 25 g acquires the velocity of 500
ms-1 after firing from the gun.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum
⟹ m1u1+m2u2= m1v1+m2v2
⟹ m1X 0+m2X 0= m1v1+m2v2
⟹ m1u1+m2u2= m1v1+m2v2
⟹0=12.5+5 v2
⟹v2=−12.55=−2.5ms-1
The negative (- ve) sign shows that the gun moves in the opposite
direction of the bullet.

12.
Questions related to law of conservation of momentum
Q2. There are cars with masses of 4 kg and 10 kg respectively that are at rest. The
car has a mass of 10 kg and moves towards the east with a velocity of 5 m.s-1.
Find the velocity of the car with a mass of 4 kg with respect to the ground.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum
Solution:
Given,
m1 = 4 kg m2 = 10 kg v1 = ? v2 = 5 m.s-1
P initial = m1u1+m2u2 = 0, (u1 = 0, u2 = 0)
P final = p1 + p2 = m1v1+m2v2

13.
Questions related to law of conservation of momentum
Q2. There are cars with masses of 4 kg and 10 kg respectively that are at rest. The
car has a mass of 10 kg and moves towards the east with a velocity of 5 m.s-1.
Find the velocity of the car with a mass of 4 kg with respect to the ground.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum
Solution:
P final = m1.v1 + m2.v2
= (4 kg).(v1) + (10 kg).(5 m.s-1)
We know from the law of conservation of momentum that, P initial = P final
⟹0=4 kg.v1+50 kg.m.s-1
⟹ v1 = -1.25 m.s-1
m1u1+m2u2= m1v1+m2v2

14.
Questions related to law of conservation of momentum
Q3.Why does the gun recoil when bullet is fired?
Date- 06/12/2022 Subject-Science Duration-35mi
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum
I. What are the two objects here?
Ans : Gun and bullet.
II. What is the initial velocity of gun and bullet?
Ans :Initial velocity of gun and bullet is zero.

15.
Questions related to law of conservation of momentum
Q3.Why does the gun recoil when bullet is fired?
Date- 06/12/2022 Subject-Science Duration-35mi
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum
III. Taking the mass of gun=m1, mass of bullet =m2,
find the final velocity of the gun if bullet moves with
velocity v1, After fired .(apply law of conservation of
momentum)
Ans:
By law of conservation of momentum,
initial momentum= final momentum. P initial = P final
⟹ m1u1+m2u2= m1v1+m2v2
⟹ m1 X 0+m2 X 0 = m1v1+m2v2
⟹ 0 = m1v1+m2v2
⟹ v1 = -m2v2 /m1

16.
Evaluation
According to law of conservation of momentum,
Initial________ = final __________________
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum

17.
Evaluation
According to law of conservation of momentum,
Initial momentum = final momentum
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum

18.
Conservation of momentum in elastic
collision
Elastic collision :elastic collision is the
collision in which there is no net loss in
kinetic energy.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum

19.
Objective : Conservation of momentum
in elastic collision
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Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum

20.
Link- https://www.physicsclassroom.com/Physics-
Interactives/Momentum-and-Collisions/Collision-
Carts/Collision-Carts-Interactive
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Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum

21.
Steps of the experiment.
• Step1. Select the mass of object 1.
• Step 2.Select the initial velocity of the object
• Step3. Select the mass of object 2
• Step4. Select the initial velocity of object 2.
• Step5. Select elastic collision.
• Step6. Click on the start button.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum

22.
Observation table
Table
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum
Before
collision
After collision
Mass of object1= 2kg u1= 5m/s v1=2m/s
Mass of object 2= 2 kg u2= 2m/s v2= 5m/s
Momentum mv 10+4 4+10

23.
Ques. What do you observe from the
observation table?
Ans. Initial momentum= final momentum
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum

24.
Result
As there is no external force acting on two bodies, the total
momentum of the system remains conserved.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum

25.
Evaluation
Ques 1.Calculate the recoil velocity of a gun
having mass equal to 2kg, if a bullet of 0.5 kg
acquires the velocity of 500 ms−1 after firing from
the gun.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum

26.
Summary

27.
Home work
Ques 1. Calculate the recoil velocity of a gun
having a mass equal to 12 kg, if a bullet of 5 kg
acquires the velocity of 5ms−1 after firing from the
gun.
Date- 06/12/2022 Subject-Science Duration-35min
Class-9th Branch – Physics Period – 2nd
Topic : Conservation of momentum