You go shopping at Ikea and come home with the cabinet pictured. The cabinet hei

Question

You go shopping at Ikea and come home with the cabinet pictured. The cabinet height is 70 cm, the depth is 20 cm, the width is 70 cm and the empty mass is 13.20 kg. The load capacity of each shelf (including the bottom) is 5 kg.You wish to hang it on your wall, but you have only two screws and are worried that they might not be strong enough.

1. Where should you attach the screws to the cabinet? Why?

2. What will the force on the screws be when the cabinet is loaded to capacity?

3. If you are screwing into a wall made of 3/8 inch wallboard, and you are using a 1/8inch diameter polly fasteners (see http://www.powers.com/pdfs/plastic/02105.pdf), will it hold? How do you know? If they will not hold, how are they most likely to fail?

Explanation / Answer

1) The screws should be attached on upoer corners so as to nullify the torque due to cabinate weight and torque due to reaction fron the wall.

2) Full capacity load, P = 5*3 +13.20 = 28.20 kg = 62.17 lbs

force on each screw, F =P/2 = 31.08 lbs

3) Ultimate load capacity for polly with 1/8 in diameter in 3/8 in wallboard is 80 lbs(tension) and 110 lbs(shear).

Alllowable load capacity for polly with 1/8 in diameter in 3/8 in wallboard is 20 lbs(tension) and 30 lbs(shear).

Here force F ( 31.08 lbs) is exceeding the allowable limit which is 30 lbs( shear) for factor of safety 4.0,

but is less than ultimate load capacity , 110 lbs ( shear).

Yes it will hold but with reduced factor of safety.

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