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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
Aims
Define momentum.
Describe experiments to demonstrate the principle of conservation of momentum
State and use the principle of conservation of momentum to solve problems.
Understand the action of rocket and jet engines.
State the relationship between force and rate of change of momentum and use it to solve problems.
Use the definition of impulse to explain how the time of impact affects the force acting in a collision.

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Momentum
IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
Main content

Conservation of momentum
Explosions
Rockets and jets
Force and momentum
Sport: impulse and collision time
Practical work: Collision and momentum
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)

1. Definition of momentum
Momentum is a useful quantity to consider when bodies are involved in ……………. and…………………




collisions
explosions
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)

1. Definition of momentum
It is defined as the mass of the body ………………….. by its velocity and
It is measured in kilogram metre per second (kg m/s) or newton second (N s).




multiplied
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)

2. Practical work
What is the momentum before the collision and after it in each case?
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)

2. Practical Work
 
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
2. Practical work






 
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)

2. Practical Work
 
20
80
40
60
20
20
20
20
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
2. Practical work






 
20,01
40
60
79,98
6,67
10
12
13.33
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
3. Conservation of momentum
When two or more bodies act on one another, as in a collision, the total momentum of the bodies remains ………………, provided no external forces act (e.g. friction).
This statement is called the principle of conservation of momentum




constant
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
3. Conservation of momentum
Example:
Suppose a truck of mass 60 kg moving with velocity 3 m/s collides and couples with a stationary truck of mass 30 kg. The two move off together with the same velocity v which we can find.






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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
3. Conservation of momentum
Solution:
Total momentum before is
(60 kg × 3 m/s) + (30 kg × 0 m/s) = 180 kg m/s
Total momentum after is
(60 kg + 30 kg) × v = 90 kg × v
Since momentum is not lost
90 kg × v = 180 kg m/s   or   v = 2 m/s







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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
4. Explosions
Momentum is a vector since it has both …………………….. and ……………………….
Momentum is conserved in an explosion such as occurs when a rifle is fired.






magnitude
direction
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
4. Explosions
Before firing, the total momentum is …………. since both rifle and bullet are at …………...
During the firing the rifle and bullet receive …………….. but ……………….. amounts of momentum so that the total momentum after firing is zero.





opposite
equal
rest
zero
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
3. Explosions
For example:
If a rifle fires a bullet of mass 0.01 kg with a velocity of 300 m/s. Find velocity of rifle
Solution:
Forward momentum of bullet = 0.01 kg × 300 m/s = 3 kg m/s
Backward momentum of rifle = 3 kg m/s
If the rifle has mass m, it recoils (kicks back) with a velocity v such that
mv = 3 kg m/s
Taking m = 6 kg gives
v = 3/6 m/s = 0.5 m/s.






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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
4. Rockets and jets
In both, a high-velocity stream of hot gas is produced by burning fuel and leaves the exhaust with large momentum.
The rocket or jet engine itself acquires an ……………… forward momentum


 


equal
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
5.Force and momentum
If a steady force F acting on a body of mass m increases its velocity from u to v in time t

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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
5.Force and momentum
We also have:


Therefore
F.t = m.v − m.u
Where
m.v is the final momentum,
m.u is the initial momentum and
F.t is called the …………………….

 



impulse
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
6. Sport: impulse and collision time




The force applied then acts for a longer time, the impulse is …………….. and so also is the gain of momentum (and …………………….) of the object
 



greater
velocity
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
7. Problem



Delphine hits a 0.050-kg golf ball, giving it a speed of 75 m/s. What impulse does she impart to the ball?
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Momentum

IGCSE Physics > General Physics > Momentum(Definition of momentum, Conservation of momentum, Explosions, Force and momentum,)
7. Problem





Solution:
Because the impulse equals the change in momentum
It is understood that the ball was initially at rest, so its initial speed was 0 m/s. Given: m=O.O50 kg
v=75m/s
So
The impulse = (0.050 kg x 75 m/s) = 3.8 kg. m/s