Dynamics Flashcards
How does the helicopter blades propel the helicopter upwards/enable it to fly wtv
Moving blades transfer momentum to surrounding air layers. By N2L, rate of change of momentum of air layers = downward force on air layers by the blades. By N3L, an upward force of same magnitude acts on the blades by air layers. Since the upward force > weight of helicopter experiences a new F upwards.
Hence, it acc upwards
N1L
A body continues in its state of rest or uniform motion in a straight line, unless a resultant external force acts on it
N2L
The rate of change of momentum of a body is proportional to the resultant force acting on it and occurs in the direction of the force
N3L
If body A exerts a force on body B, then body B exerts an equal and opposite force on body A
Eqn for Fnet
Fnet = d p / d t = d (mv) / dt = m (dv / dt) + v (dm / dt)
Unit of Fnet
Kg m s^-1 OR Ns
Momentum eqn & symbol
p = mv
Impulse eqn & defn & how to read from graph
Δp = m Δv
= m (Vf - Vi)
= F Δt
Impulse is the product of the force F acting on an obj and the time of impact
Area of F-t graph
Properties of action rctn pair
- equal in mag
- opp in direction
- same nature of force
- act on diff bodies
Defn of inertia
Reluctance to start moving/change its motion
Defn of weight
Force experienced by a mass in a gravitational field
What musttt u write when calc force on space craft when gas is ejected
By N3L, |force on space craft| = |Force on gas| =…
Principle of conservation of momentum
Total linear momentum of a system of interacting bodies remain constant provided no external resultant force acts on the system
Defn of Elastic collision
Relative speed of approach of bodies is equal to the relative speed of separation of bodies
Head-on elastic collision
Direction of motion of the bodies after collision is along the same line of motion (w/o any deviation from org path)
Qn: If a car has a crumple zone, how does it protect passengers
FΔt = Δm v
since t increases, F decreases and this protects passengers since ave force decreases
Qn eg on mass splitting into 2 and fall (opp directions) - what happens to the time for each mass to reach the ground?
remain the same
Elastic VS Inelastic VS Completely inelastic collision
Elastic - momentum & KE conserved
Inelastic - Momentum conserved, KE not
Completely inelastic - Obj stuck together after collision –> move off at the SAME SPEED after collision
eqn for conservation of linear momentum
m1u1 + m2u2 = m1v1 + m2v2
Eqn for conservation of KE
1/2 m1u1^2 + 1/2 m2u2^2 = 1/2 m1v1^2 + 1/2 m2v2^2
Special eqn for elastic collisions only
u1 - u2 = v2 - v1
4 cases of interest for elastic collisions
case 1 m1 = m2 v1 = u2 & v2 = u1
case 2 m1 = m2 & u2 = 0 v1 = 0 & v2 = u1
case 3 m1<>m2 & u2 = 0 v1 ~ u1 & v2 ~ 2u1
Defn of linear momentum
Linear momentum of an obj is defined as the product of its mass and its velocity
How to change of KE from momentum - eqn?
Ek = 1/2 mv^2 = 1/2 m^2v^2/m = p^2/2m
