what is the value of these angles ?

i know that question is a little basic but i have no one to ask.

for this image i think that the angle of the normal force that the semi-cylinder
exert on the bar is is α – 90°

Original Image


Spoiler




for this one i think that the angle of the normal forces that the cylinders exert on the bar is O – 90°

but my teacher says that is O and i can’t figure why.

some one can explaimed why ? thanks.

Original Image


Spoiler




http://ift.tt/Ou0NXV

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