Acetylcholine competes to bind to the same G protein as noradrenaline, thereby reducing the available receptors for noradrenaline to bind to

Acetylcholine binds to the G protein causing a conformational change that prevents noradrenaline from binding

Acetylcholine binds directly to noradrenaline meaning it cannot bind to further receptors

Both neurotransmitters act on the same G protein that have differing effects on adenyl cyclase in the heart

They each activate a different G protein which in turn acts on adenyl cyclase in the heart