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A level physics mechanics question (1)

why is it C ? C isnt even on the card so how can that be the centre of mass of the card ? IMG_6977.jpeg
(edited 1 month ago)
Reply 1
Since the card is suspended from a point, the center of mass must be somewhere on the plumb line; namely, the CoM can only be A, C or D.

If you look at point D, you can clearly see that, although the mass is balanced on the horizontal axis, it is not balanced in the vertical axis: the bulk of the card is above this point, so it cannot be the CoM! Similarly with A, the bulk of the mass is located below this point. This leaves point C.

Intuitively, imagine rotating the card by 90 degrees and suspending it from points A or D: it would tip over.
(edited 1 month ago)

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