Physics class 9
Chapter number 3
Dynamics
Comprehensive Questions
Question No 03
What is weight? Differentiate between mass and weight?
Answer
The differences between mass and weight is given below.
Mass
1)Mass definition: mass is the amount of the matter in an object.
2) Quantity: Mass is a scalar quantity.
3) Measurement: Mass is usually measured in grams and kilograms.
4) Measurement tool :It is measured by beam balance.
5) SI Unit :The SI unit of mass this kg ( kilogram).
6) Representation: Mass is represented by "m".
7)Value: Its value can never be zero.
8) Physical Quantity: It is a base physical quantity.
9) Remaining: It remains same or constant everywhere.
10) Formula : F= ma
m= F/a
VS
Weight
1) Weight Definition: weight is a force in which the earth attract a body toward it's center.
2) Quantity: weight is a vector quantity.
3) Measurement: weight is measure in Newton (N).
4) Measuring Tool: it is measured by spring balance.
5) SI unit : The SI unit of weight is Newton ( N).
6) Representation: it is represented by (w)
7) Value: it's value can be zero.
8) physical quantity: it is a derived physical quantity.
9) Remaining: it cannot Remain same or constant everywhere it changes with altitude.
10) Formula: w = mg
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Question No 04
Define momentum ? relete force to change in momentum.
Movementum : The quantity of motion contain in an object is called momentum.
Linear movementum : the product of mass and velocity is called linear momentum.
Quantity: momentum is a vector quantity.
SI unit : the SI unit of momentum is Newton's second (NS).
Representation: momentum is it represented by( p).
Newton's second law and momentum:
Force and momentum: The time rate of change of momentum must be equal to the net force acting on the body.
Mathematically: by the definition of Newton's second law of motion.
F = ma ............. equation (1)
a = vf-vi/∆t.............. equation (2)
Put equation 2 in equation 1.
F= m (Vf-Vi)/∆t
F= mvf-mvi/∆t .............. equation (3)
Where mvf-mvi/∆t = ∆p
Put in equation No 3
F= ∆p/∆t
Hence it is proved that change in momentum is equal to the net force.
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Question No 5
Define isolated system. Explain the love conservation of momentum.
Answer
Isolated system: An isolated system is a group of interacting bodies on which no external force acting.
Law of conversion of momentum: This law states that the momentum of an isolated System of two are more than two interacting bodies remains constant this is called the law of conservation of momentum.
Mathematically: F=∆p/∆t
For isolated system F= 0
Then. 0 = ∆p/∆t
0×∆t = ∆p
0 = Pf-Pi
Pi = Pf
Thus in the absence of external force of an isolated system the initial momentum (pi) will be equal to final momentum (pf) and the total momentum of the system cannot be change but remains constant.
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Question No 06
Define collision and explosion. Explain change in momentum in terms of collision and explosion.
Answer
Collision: The phenomenon in which two particles come close to each other and interact each other by means of some forces is called collision.
Explosion: An explosion is a sudden and an intense release of energy that often produces a loud noise and high temperature.
Change in momentum in terms of collision and explosion: momentum is conserved in all type of explosions and collisions.
Pi= Pf
Movement of a partical before collision or explosion= momentum of particle after collision or explosion.
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