2 Angular Momentum and 1 Rotational Inertia Question....Any Help Is Very Appreciated!?

Question

Question 1:

A 440 g hoop 200 cm in diameter is rotating at 252 rpm about its central axis. What is its angular momentum?


Question 2:

A weightlifter's barbell consists of two 35-kg masses on the ends of a 20-kg rod 1.6 m long. The weightlifter holds the rod at its center and spins it at 7 rpm about an axis perpendicular to the rod.
What is the magnitude of the barbell's angular momentum?

Question 3:

Engineers redesign a car's wheels with the goal of decreasing each wheel's angular momentum by 23% for a given linear speed for the car. Other design considerations require that the wheel diameter go from 38 cm to 35 cm. If the old wheel had a rotational inertia of 0.42 kg·m2, what must be the new wheel's rotational inertia if the engineers are to achieve their goal?

Answer 1

H represents ang. momentum. H = Iω, ω in rad/s
1. I = mr^2
2. I = I(bar) + I(weights)
I(bar) = m(bar)L^2/12
I(weights) = 2m(weight)*(L/2)^2
3. At a given linear speed, new angular rate ωf = 38/35 * old angular rate ωi, and
Hf = 0.77Hi
If*ωf = 0.77Ii*ωi
If*38/35*ωi = 0.77*0.42*ωi
If = 35*0.77*0.42/38 kgm^2