A heavy flywheel rotating on its central axis is slowing down because of friction in its bearings. At the end of the first minute of slowing, its angular speed is 0.70 of its initial angular speed of 125 rev/min. Assuming constant frictional forces, find its angular speed at the end of the second minute.

ωf' =5.16 rad/s

Explanation:

Given that

Initial angular speed ,ωi= 125 rev/min    ( 1 rev/min = 0.10472 rad/s)

ωi=13.08 rad/s

The angular speed after 1 min ,ωf= 0.7 x 125 = 87.5 rev/min

ωf=9.1 rad/s

Lets angular acceleration =α

We know that

ωf = ωi + α t

Now by putting the values in the above equation we get

9.1 = 13.08 + α x 60             ( after 1 min ,t= 60 s)

α = -0.066 rad/s²

The angular speed after 2 min

ωf' = ωi + α t

ωf' =13.08 - 0.066 x 2 x 60 rad/s

ωf' =5.16 rad/s

Therefore the angular speed after 2 min will be 5.16 rad/s.

it is the second option.

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.