It's easy once you know where to throw the bombs. Run to the second bomb first and throw it to the gold "bolt" in the floor. Pick up the bomb from the first position and toss it slightly to the left of the bolt. These two will blow up the first 5 trash piles. Quickly pick up the bomb from the third spot and throw it to the next gold bolt, it's the one towards the center. Grab the 4th bomb and throw it to the gold bolt farthest right. Run back and get another bomb and throw it slightly to the right of the last bomb and it will take out the remainder. Check out videos on youtube for a visual. It took me a couple of days to get that rythym, but now I can do it no problem. Hope this helps.
Also, if you are running out of time (less than 9 seconds) and have a bomb close but not quite right, throw another bomb to set up a chain reaction. The bombs take 9-10 seconds to explode, but if they're close enough to one about to explode, you can blow up 2-3 more in the final seconds that otherwise would not have exploded.
One other tip I've learned while playing through again. If you run into the bombs without picking them up, you'll trigger the fuse, so you can run into them before 11 seconds remaining but not place them until just before they blow. Makes the star a lot easier to get than trying to set up chain reactions.
this star is one of the only ones i cannot beat by myself. I can't even find out the difference between this one and the one in the battlerock galaxy, but they managed to make this one a lot harder. why is it so impossible?