(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A non-uniform plank of wood AB has length 6m and mass 90kg. The plank is smoothly supported at its two ends A and B, with A and B at the same horizontal level. A woman of mass 60kg stands on the plank at the point C, where AC=2m. The plank is in equilibrium and the magnitudes of the reactions at A and B are equal. the plank is modelled as a non-uniform rod and the woman as a particle. Find

(a) the magnitude of the reaction on the blank at B,

(b) the distance of the centre of mass of the plank from A.

2. Relevant equations

- general knowledge on moments.

3. The attempt at a solution

(a) i was going to take moments about the point A, therefore as the reaction force (R) at A acts through A its moment will = 0, therefore allowing me to find the reaction force (R) at B knowing the moment of the woman at A is (60g* x 2) *where g=9.8, but as the rod is non uniform i can't assume the rods mass (90kg) acts at the centre, i.e. 3m away from A (therfore the moment at A can't be 90g x 3), therefore i don't know how to take this into account without creating a distance X for the mass from A, which would only lead me onto part B anyway.

???

Thanks Mike.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: As level mechanics unit 1 question on moments.

**Physics Forums | Science Articles, Homework Help, Discussion**