I am trying to get cpu util and memory occupied for a process. I use these (I am showing output also):

using top
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$ top p 25272 d 5
top - 01:52:17 up 2 days, 21:28, 2 users, load average: 0.02, 0.05, 0.06
Tasks: 1 total, 0 running, 1 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.0% us, 0.0% sy, 0.0% ni, 100.0% id, 0.0% wa, 0.1% hi, 0.0% si
Mem: 4147560k total, 1628824k used, 2518736k free, 37320k buffers
Swap: 0k total, 0k used, 0k free, 244200k cached

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
25272 911 16 0 1431m 1.1g 22m S 0.0 28.3 131:51.55 java

using ps
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$ ps -p 25272 u
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
911 25272 50.3 28.3 1465912 1175352 ? S Mar01 131:51 /usr/java/jre-1

Question - why does these 2 programs show different utilization for the same process ? ps is showing 50.0 % whereas top is showing 0.0 %.