Cylindrical fishing reel problem using moment of inertia

[jhart_929]

Homework Statement

A cylindrical fishing reel has a mass of 0.85 kg and a radius of 4.5 cm. A friction clutch in the reel exerts a restraining torque of 1.6 N·m if a fish pulls on the line. The fisherman gets a bite, and the reel begins to spin with an angular acceleration of 66 rad/s2.
a) Find the force of the fish on the line.
b) Find the amount of line that unwinds in .5 seconds.

Homework Equations

I = .5mr^2
theta = .5at^2

The Attempt at a Solution

I found the moment of inertia to be 8.606. What I don't understand is how to relate the torque to the moment of inertia. I don't know if my calculator should be set to radians or degrees, but I tried both ways and got them both wrong.

 

[LowlyPion]

First of all I needs to be calculated with the radius as .045. That makes your I off by a factor of 10⁴

I = 8.6*10^-4

T = a*I

So accounting for the force on the line and the restraining force ...

F*.045 = 1.6 + 66*8.6*10^-4

You have the right equation for b. Just remember that since θ is in radians, you need to provide θ*r for the length of line that reels off.

 

[LowlyPion]

A useful rotational kinematic link:
http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html#rlin

 

[jhart_929]

Alright thanks so much! I understand how to do it now!