Thats pretty useless. Unless they see how many lives can be taken with just one bomb the Japanese wouldn't have surrender. Both Nagasaki and Hiroshima was densely populated cities and a prime target (shock targets) to show their "1 bomb 1 city" principle. See how the Japanese didn't surrender after the first a-bomb was dropped?If the bomb was dropped in a demonstaration though and not over populated land the war could have possibly ended with no/minimal calualties on both sides.
Think of it this way, its 1945 and you are the US President, remember you are at war with the Japanese which attacked Pearl Harbor. You have 2 atomic bombs at your disposal, "1 bomb 1 city" and back then no one knows the after effect of the a-bomb or if they did, it didn't matter. If you were to invade Japan you will need the support of the Soviets, cause America alone would have a hard time fighting against them, losing thousands of American lives. If I was the President back then would i send my soldiers to fight a war which we might lose without the help of the Soviets? Or rather ending it quickly without losing any of the lives of my people? We saw what happen to Germany after the war, Democracy and Communism can't go together. Remember you are the US President and your countries people are more important than the enemies. Everything adds up to dropping the bomb on Nagasaki and Hiroshima. Only 2 person in the US military objected to dropping the bomb one of them was the person responsible for D-Day forgot his name.
Now, obviously today most people would say it wasn't necessary to drop the bomb because after so many years the effect can still be seen. But if i was at war with a country and there is way end it without losing any of my people, I would use it.