Angular rotation question
Hi, I am massively stuck on the following question and am examined on this stuff soon, could someone please help me?
A thin, uniform 15kg post of length 1.75 m is held vertically using a cable attached to the top of the post. A string attached to a 5kg mass passes over a smooth, massles pulley and is attached to the post 0.5m from the top. The post has a pivot at the bottom of it (i.e. that is what it rests on). Suddenly the cable snaps.
a. Find the angular acceleration of the post (with respect to the pivot) just after the cable snaps.
b.Will the angular acceleration from a be constant before the post hits the pulley? Why?
c.What is the acceleration of the 5kg mass the instant the pulley breaks? Is this constant? Why?
According to the back of my book the answers I should get are:
a. 2.65 rad/s^2
b. no, no explanation why given.
c. 3.31 m/s^2, n (no explanation given)
My attempt.
a. Torque (T)= moment of inertia (I) x angular acceleration (A)
T= 5g(1.750.5)=61.25
I= (MR^2)/4 = 15.3125
a=T/I = 4
(I don't see where I am going wrong for this part, any ideas?)
b. I think no because as the stick falls the line of action of the applied force changes and hence so does the torque. Is this explanation correct?
c. I though this acceleration was just g. As for whether it is constant I thought yes, but the answer is no.
