Find torque of a ball on the end of a light rod

[mathcrzy]

Homework Statement

A small 1.25 kg ball on the end of a light rod is rotated in a horizontal circle of radius 0.890 m.
(a) Calculate the moment of inertia of the system about the axis of rotation.
____kg*m^2
(b) Calculate the torque needed to keep the ball rotating at constant angular velocity if air resistance exerts a force of 0.0800 N on the ball.
____m*N

Homework Equations

a) kg*m^2
b) kg*m^2-air resistance (dont know the formula; just a guess)

The Attempt at a Solution

a) 1.25*.89^2=.99kg*m^2 (i was able to figure out this answer)
b) 1.25*.89^2-.08=.91m*N

 

[saket]

Hint: air resistance is a force, you are required to find torque. how do u corelate them?

 

[FedEx]

Do you know how to find find the Moment of inertia?

 

[GTrax]

You got the moment of inertia right.
Carefully consider what forces it faces when moving at constant angular velocity.

 

[FedEx]

Find the torque which is applied by the air on the object.The same amount of torque should be applied in the opposite direction in the opposite direction.

Torque = force * radius