Tag Archives: round

A mass of 0.380 kg hangs from a string wound round the cylinder.
(a) when the system is released from rest, the mass takes 2.0 s to fall through a height of 5 m. What is the moment of inertia of the cylinder?
(b) The cylinder is then replaced by a hollow cylinder of the same mass and dimensions. Discuss qualititively the effect on (i) the speed of the mass (ii) the rotational kinetic energy of the cylinder, when the mass falls through a height of 5 m
Let me break down the question one by one.

First of all, may I say that I alpha equals FR since Tau = I alpha
= F R?

Secondly, to get alpha, I need final angular velocity. wf

In order to get w, I shall get it from v = rw, v get from mgh = 1/2 m

v^2, therefore v = square root of 2gh, hence w = square root of 2gh

over r.

So the wi = 0 cos its from rest, t = 2. then alpha = 27.5 rad/s^2

The following shall be I = FR/alpha = mghr/27.5

Will I get I = 0.122, but the book answer says 0.0360.

(The question assumes we do not know that moment inertia for a
cylinder is 1/2
mr^2)

I need the answer for (a) in figures. Thanks