Dynamics

Question 1

How does the helicopter blades propel the helicopter upwards/enable it to fly wtv

Answer 1

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

Question 2

N1L

Answer 2

A body continues in its state of rest or uniform motion in a straight line, unless a resultant external force acts on it

Question 3

N2L

Answer 3

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

Question 4

N3L

Answer 4

If body A exerts a force on body B, then body B exerts an equal and opposite force on body A

Question 5

Eqn for Fnet

Answer 5

Fnet = d p / d t = d (mv) / dt = m (dv / dt) + v (dm / dt)

Question 6

Unit of Fnet

Answer 6

Kg m s^-1 OR Ns

Question 7

Momentum eqn & symbol

Answer 7

p = mv

Question 8

Impulse eqn & defn & how to read from graph

Answer 8

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

Question 9

Properties of action rctn pair

Answer 9

1. equal in mag
2. opp in direction
3. same nature of force
4. act on diff bodies

Question 10

Defn of inertia

Answer 10

Reluctance to start moving/change its motion

Question 11

Defn of weight

Answer 11

Force experienced by a mass in a gravitational field

Question 12

What musttt u write when calc force on space craft when gas is ejected

Answer 12

By N3L, |force on space craft| = |Force on gas| =…

Question 13

Principle of conservation of momentum

Answer 13

Total linear momentum of a system of interacting bodies remain constant provided no external resultant force acts on the system

Question 14

Defn of Elastic collision

Answer 14

Relative speed of approach of bodies is equal to the relative speed of separation of bodies

Question 15

Head-on elastic collision

Answer 15

Direction of motion of the bodies after collision is along the same line of motion (w/o any deviation from org path)

Question 16

Qn: If a car has a crumple zone, how does it protect passengers

Answer 16

FΔt = Δm v

since t increases, F decreases and this protects passengers since ave force decreases

Question 17

Qn eg on mass splitting into 2 and fall (opp directions) - what happens to the time for each mass to reach the ground?

Answer 17

remain the same

Question 18

Elastic VS Inelastic VS Completely inelastic collision

Answer 18

Elastic - momentum & KE conserved
Inelastic - Momentum conserved, KE not
Completely inelastic - Obj stuck together after collision –> move off at the SAME SPEED after collision

Question 19

eqn for conservation of linear momentum

Answer 19

m1u1 + m2u2 = m1v1 + m2v2

Question 20

Eqn for conservation of KE

Answer 20

1/2 m1u1^2 + 1/2 m2u2^2 = 1/2 m1v1^2 + 1/2 m2v2^2

Question 21

Special eqn for elastic collisions only

Answer 21

u1 - u2 = v2 - v1

Question 22

4 cases of interest for elastic collisions

Answer 22

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

Question 23

Defn of linear momentum

Answer 23

Linear momentum of an obj is defined as the product of its mass and its velocity

Question 24

How to change of KE from momentum - eqn?

Answer 24

Ek = 1/2 mv^2 = 1/2 m^2v^2/m = p^2/2m