Nice value for starters. It should be clear that the payload experiences the same acceleration as the rocket. (Otherwise it would either lag or lead the rocket!)

What you seem to miss:

Hope this helps

2.93 m/s^2? Do you really believe in this value?

One of the ways to estimate is to look through Delta IV Payload Planners Guide. This is the best document to begin with.

@ Konstantin Luchnikov

Look up the data (total mass, thrust) here: https://en.wikipedia.org/wiki/Delta_IV

The initial acceleration of some 0.25 g is reasonable within mass variations.

Regards

@u.Dreher

Thank you for your answer. Yes, I understand that acceleration increases with time as the fuel is spent. The value 2.93m/s2 is the initial value with all the fuel. Thta's why I am confused as to which value to consider for analysis? The highest a rocket can achieve ?

@ Konstantin Luchnikov

Thank you for your answer. I have already considered the data in Delta IV Users guide for my calculation (weight and thrust values). The guide also says Delta IV heavy can reach a steady state acceleration of 4.3 g = 42.16m/s2 (for the payload mass that I am considering) ---> Is this value what I should use?

@ Konstantin Luchnikov

Yes, I believe this value although it seems odd. 

Check this link

https://www.nasa.gov/pdf/466711main_AP_ST_ShuttleAscent.pdf