I am having some problems starting the following problem:(adsbygoogle = window.adsbygoogle || []).push({});

A uniform plank of mass 87 kg is mounted so it can rotate about a horizontal axis as indicated in the attached picture. Two physics students with masses 60.0 kg and 80.0 kg are attached to the ends of the plank as indicated. Consider the students as particles.

(a) Calculate the moment of inertia of the system of the plank and two students about the indicated axis.

(b) What is the magnitude of the total torque acting on the system about the indicated axis arising from gravitational forces?

(c) Determine the magnitude of the initial angular acceleration of the system, assuming it is released initially at rest.

(d) Is the angular acceleration constant as the plank turns?

(e) Determine the angular speed of rotation of the system when the plank is vertical. (Assume unrealistically the students do not fall off!)

(f) What is the magnitude of the angular acceleration of the system when the plank is vertical?

I am not sure how to think of the system. When calculating the moment of inertia, is the plank considered a rod or a rectangle? There are no width measurements so I assume it is to be thought of as a rod. If this is correct, then how do I find part (a)?

I would think I would use the equation:

I = (1/12)*(M)*(L)^2 but I am not sure if I count the students as part of the total mass of the plank or if I must add their moments of inertia seperately like this:

I(plank) + I(student1) + I(student2) = I(total) for part (a).

Any advice?

Thanks!

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# Homework Help: Calculate the moment of inertia of the system

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