Hi, I have hard time understanding the rotational inertia . A string is wrapped around a cylindar spool of radius 1cm. The axis of the spool is fixed. A length of string of .8 m is pulled off in 1.5 s at a constant tension of 20N. What is the rotational inertia of the spool? Can I have some help with this problem? I don't know how to start. The only definition of rotational inertia I have is I=mR2! Thank you B.