Three solid, uniform flywheels, each of mass 65.0 kg and radius 1.47 m, rotate independently around a common axis. two of the flywheels rotate in one direction at 3.83 rad/s; the other rotates in the opposite direction at 3.42 rad/s. calculate the magnitude of the net angular momentum of the system.

297.77 kg m^2 / s

Explanation:

mass of each flywheel, m = 65 kg

radius of flywheel, r = 1.47 m

ω1 = 3.83 rad/s

ω2 = - 3.42 rad/s

Moment of inertia, I = 1/2 mr² = 0.5 x 65 x 1.47 x 1.47 = 70.23 kg m^2

Angular momentum is defined as

L = I x ω

Net angular momentum

L = 2 x I x ω1 - I x ω2

L = 2 x 70.23 x 3.83 - 70.23 x 3.42

L = 537.96 - 240.19

L = 297.77 kg m^2 / s

Thus, the angular momentum is 297.77 kg m^2 / s.  

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s

there are no contact forces mentioned on the list of choices that you've provided.