Hi Vijay,
On the FWSM, you can look at the output of 'show traffic' and 'show interface' to get a rough idea of the amount of traffic passing through these interfaces over time. You can use 'clear traffic' and 'clear interface' to reset the counters to 0.
A better solution for gathering this type of data would be to enable NetFlow on the switch where the FWSM is installed. This will give you more granular and trackable statistics over time.
Hope that helps.
-Mike
