Osaka/Hiroshima in 1/2 day?

Can i do Osaka Hiroshima in say 5 hours including the Peace Museam and A Bomb dome or am i pushing it? My idea was to leave around noon from OSaka and back late aftermoon thanks

It could be done, the travel time, would consume a great deal roughly 3 of the 5 hours.
Once in Hiroshima, the dome is 10 min street car ride, and the museum is about a 10 minute walk from there. The dome takes no time to see, its just there, and the museum I would say at a easy pace about 45mins to walk though.

Hiroshima is among my favorite cities in Japan, clean, pretty and peaceful, yet still a modern city. Its not a place I would just rush though, Osaka however, personally I find little reason to hang around the area :)

I suppose if you specifically want to see the Peace Park, then it's doable.

If you want to see Miyajima Island though, which IMHO is the best bit of seeing Hiroshima, you wont have nearly enough time.

If you are going in the near future, be aware that the sun goes down early right now. I was in Japan a couple of weeks ago and sunset was 4:30 as starting to get dark at 3:30. This messed up my plans several times.

Osaka? Hey, Dotombori is a fun little road to walk along. Best to see it in the evening.

Finally, as I write in the title, things always take longer than you plan. Waits for trains, figuring stuff out, stopping for food. IMHO, don't try and squeeze things too much. It doesn't work out.

The shinkansen ride from Shin-Osaka to Hiroshima takes 80 minutes by nozomi. 95 minutes by hikari.

Then, it takes about 25 minutes from the platform to the closest tram stop to the peace park. Another 5 minutes to reach the peace museum.

Add another 10-30 minutes for the trip from central Osaka to Shin-Osaka Station.

So, in total, you should allocate about 2.5 hours for the one way trip from central Osaka to the peace museum. That is already 5 hours for the round trip, not including the time you have to wait for the next shinkansen departure.

If you want to see the peace museum and nothing else, I recommend to allocate at least around seven hours to your side trip to Hiroshima.

Costwise it would be very expensive unless you have a Japan Rail Pass.