Been reading and knew these two will be near earth soon. Especially YU55 which is much nearer to us than ever. I am fearful to what if, just what if they hit onto earth?
'Near' does not equal 'right on top of' - the Moon is near to us, much much much nearer than the closest Comet Elenin will ever get. Do you fear the Moon for being so close? YU55 gets closer to the Earth than the Moon, but would still mean a two or three day journey inside an Apollo command module for you to be able to get within touching distance (and by the time you manage that it'll have already flown past and be off on it's merry way through the solar system).
It's important to get a perspective on distances in space. 'Near' and 'far' mean different things to different people. Mars is absolutely miles away, it'd take months to get there, but it's in our backyard compared to Gliese 876d. Mars is a stones throw away compared to the nearest planet to us that orbits another star (15 light years, if you're interested). Something can feel 'near' even when it's actually really far away.
When a comet or asteroid hit earth, it won't flatten the whole of earth but when hit onto ground, what will the impact be?
If you want to have some fun you can try out a number of impact simulators for yourself, to get an idea of what a 'successful' impact can achieve, if those are the right words to use. The point is you can see for yourself what an icy comet can do compared to a dense asteroid, whether scale has any factor, speed and so on. You can - if you know them - plug in the numbers and characteristics for Elenin and YU55 and see what they would do if they were ever to hit Earth, which they won't be doing within your lifetime.
That's the important part to remember. It's all well and good finding out how big a hole in the ground an asteroid will make, but if you don't understand that the object in question won't hit in the first place, it may end up driving fear up a notch instead of quelling it.
Just wanna know the estimated distance of impact will be for comet elenin and asteroid yu55?
Again, for emphasis, neither of these objects have a chance of impact with Earth. For a more detailed, interesting look at YU55, check out this article over on Bad Astronomy - note that it doesn't go into detail about impacts and whatnot because that's not what is interesting about the asteroid, it's not a concern for this pass.
I have been anxious and unable to eat or sleep well the past few days worrying abt the comet and asteroid and what happen and how far should we be safe from the impacted area.
You can sit on a sun-lounger in your back yard and enjoy the sights. Well, in an ideal world. The initial thoughts of Elenin being nice and bright have gradually tended towards it being juuuuust on the edge of naked eye visibility when it's at it's closest. YU55 will probably pass without you remembering it was going to pass in the first place, it'll be that quick a blip - I might even sleep through it, depends when on the 8th it'll be passing.
But the point is, these are not events to run away from. If you're going to run in a certain direction, run outside to get a better view. Far more asteroids pass closer than these two objects do and we only find out days in advance, but they're teeny tiny little things that are gone before you know it. Every time you see a shooting star you're seeing anything from a grain of sand to a chunk of rock scream through the atmosphere, sometimes if they're big enough managing to land somewhere. You don't fear these do you? You perhaps don't even know about them.
These big guys you mention have already been spotted, are already being tracked, and have already been shown to have no chance of impact, months ahead of when they'll be at their closest. Just need to sit back and wait, hope they offer some good sightseeing towards the end of the year.