Dynamics Flashcards
Define mass of a body
The measure of its resistance to change it’s state of motion
Define momentum of a body
The product of it’s mass and it’s velocity
Force acting on a body is defined as
the rate of change of momentum of the body
Formula for force
F = (dP)/(dt)
Impulse is
The product of the force acting on a body and the time of impact on the force
Ft
N1L
a body will continue to be at rest or continue to move at constant velocity unless a resultant external force acts on it
N2L
The rate of change of momentum of a body is proportional to the resultant external force exerted on it and the change in momentum is in the direction of the force.
N3L
When body A exerts a force on body B, body B exerts an equal and opposite force on body A.
Principle of conversation of linear momentum
The total momentum of the bodies in the system remains constant if there is no resultant external forces acting on it
Formula for principle of conservation of linear momentum
M1U1 + M2U2 = M1V1 + M2V2
Formula for elastic collision
U1 + U2 = V2 - V1
For KE to be fully conserved (formula)
½m1(u1)^2 + ½m2(u2)^2 = ½m1(v1)^2 + ½m2(v2)^2
Derive impulse from the equation of momentum/
p = mv
F = dp/dt
Impulse = Ft
Derive U1 - U2 = V2 - V1
For momentum to be conserved, m1u1 + m2u2 = m1v1 + m2v2 - (1)
For kinetic energy to be fully conserved, ½m1u1² + ½m2u2² = ½m1v1² + ½m2v2² - (2)
From (1) - m1(u1-v1) = m2(u2-v2) - (3)
From (2) - m1(u1²-v1²) = m2(u2²-v2²) - (4)
(4)/(3):
u1+v1= u2+v2
u1-u2 = v2-v1
State what is meant by an inelastic collision between 2 objects by reference to the speed of the objects.
Relative speed of approach before collision ≠ relative speed of separation after collision.
State what is meant by an inelastic collision between 2 objects by reference to the energy of the objects.
Total initial KE ≠ total final KE and is transferred to other forms of energy.
(NOT “energy is conserved”)
Why does a falling object reach constant velocity?
Air resistance, which acts opposite to the object’s motion, increases as speed of object increases.
Resultant force on the object which is the difference in it’s weight and air resistance, would decrease as the object falls.
Eventually, when magnitude of air resistance is equal to the object’s weight, resultant force = 0 and by N2L, acceleration = 0 and object reaches constant velocity.
