# Homework Help: Falling plate

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1. Aug 3, 2015

### Alex.malh

1. The problem statement, all variables and given/known data
A plate is fixed to the ceiling by two wires and to the wall by a single wire.
The wall wire is cut. Calculate the tension in the two remaining wires.

mass = 800 kg
g = 10m/s²
Dimensions in sketch

2. Relevant equations

3. The attempt at a solution
Equations:
Ra*cos30 + Rb*cos30 = m*g + m*av
Ra*sin30 + Rb*sin30 = -m*ah
ah*sin30/cos30 = av

Solve to:
(Ra+Rb)=6928N
ah=-4.33m/s²
av=-2.5m/s²

But now i'm having troubles getting the individual wire tensions.
Any help is welcome.

Thank you.

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2. Aug 3, 2015

### SteamKing

Staff Emeritus
You know the force of gravity acting on this plate, and you have calculated the horizontal and vertical accelerations the plate experiences when the horizontal string is cut.

The tensions in the vertical wires will be a combination of the static and dynamic forces acting on the plate. You can assume these forces act thru the center of gravity of the plate, the location of which is indicated in the sketch.

To calculate the dynamic forces: (Hint: F = ma)

3. Aug 3, 2015

### haruspex

I'll offer a different hint: will the plate rotate?

4. Aug 4, 2015