Answer:
The no of revolutions rotor turn before coming to rest is 1,601.1943 and time taken is equal to 19.21 seconds
Explanation:
here we know that torque = I×α
α= angular acceleration
I = moment of inertia of hollow disc = m×
given that m=4.37kg
k=0.0710m
torque=1.2Nm


from the above equation we can calculate the angular acceleration of the hollow disc .
since 

from this above equation 
no of revolutions =
= 1,601.1943.
Now to calculate time we know that time = 
so upon calculating we will be getting t=19.21 seconds
Answer:
66.4 m
Explanation:
To solve the problem, we can use the length contraction formula, which states that the length observed in the reference frame moving with the object (the rocket) is given by

where
is the proper length (the length measured from an observer at rest)
v is the speed of the object (the rocket)
c is the speed of light
Here we know
v = 0.85c
L = 35.0 m
So we can re-arrange the equation to find the length of the rocket at rest:
