It will depend on what the walls is made of. If its brick you'll need raw plugs that are rated to the weight of the projector plus the weight of the shelf and anything else you wish to put on that shelf, I'd also add a contingency. Try to place the load on the shelf as near to the wall as possible to ensure the load is pulling straight down 5 KG isn't much. If its plaster board you'll need the plaster board fixings that are rated to the weight you wish to support.
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