[smusamashah]

After reading the title I imagined a bin I could throw things at and it suddenly opens and closes.

Would these proximity sensors alone be enough to detect a projectile coming at it?

[Izkata]

Drop the "coming at it", make it race to catch any thrown trash: http://www.youtube.com/watch?v=ZNWd4FFYDv0

[abiogenesis]

The sensors could detect that, but a motor that opens the lid so fast could be dangerous.

[adrianmonk]

Some garbage cans have lids that open inward, so I guess you could do it that way.

[Cyphase]

This comment caused me to imagine a garbage can that smacks the garbage you threw at it back at you.