more help with rotational kinematics and energy in physics?

Question

A lawn mower has a flat, rod-shaped steel blade that rotates about its center. The mass of the blade is 0.82 kg and its length is 0.56 m.
(a) What is the rotational energy of the blade at its operating angular speed of 3500 rpm? (in kJ)
(b) If all of the rotational kinetic energy of the blade could be converted to gravitational potential energy, to what height would the blade rise? (in m )

I've tried a few approaches to this problem and I seem to be stuck. Any help is greatly appreciated--thanks

Answer 1

(a) Ke=.5 Iw^2

I - moment of inertia
w- angular velocity

I= (mL^2)/12
L- length
m - mass
w=2 pi (rpm)/60= (for radians/sec)
w= 367 rad/sec

Ke= .5 ((mL^2)/12)(w)^2
Ke=.5 (( .82 (.56)^2)/12)(367)^2=
Ke=1366 Joules

b) Pe=mgh=Ke

h=Ke/mg=1366/( .82 x 9.81)=170 m

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