50w LED vs 1 plant

if you want to know if the plant would make it to the end, the answer is yes if you want to know if it will give you a good yield, it's no plus, you'd complicate everything with such a big pot with a 50W; 6/7 liters is enough also, the roots wouldn't have enough strength to cover all that soil volume

I've seen a weed plant grown inside a PC case using a T5 light with surprising success, so yes, anything is technically possible with the right time and know-how. But you're certainly not describing an ideal growing setup, so I'm not sure whether it would be worth the amount effort for the returns you'd get. What are the dimensions of this container? What would you do for air flow inside? 50W is not a lot of light, even for one plant, but the COB can't be right on top of the canopy either as you'll get light burn, so you'll need a gap between the light and the plant. You'd need the right genetics so the plant stays small and doesn't stretch. A pump feeding air to the nutrient solution. Air extraction to control humidity. There's a lot to do to get a decent yield in a space so small.

No, 50w is barely enough to sustain life in general, let alone grow decent plant/buds.

1g/watt with cob.. bit higher with a high end one like a cree .. i forget the model numbers now. 1 plant prolly do okay as ong as you don't grow it too large.