The CPU Utilization of a computer is 100%.
Is it possible to execute a new application under the above condition?
On operating systems with preemptive multitasking it is possible. The scheduler will interrupt the offending process so that other processes can get some time to run as well, but the offending process will still tend to hog the cpu and make the system feel very slow.
On OSes with cooperative multitasking it is only possible if the process which is using 100% of the CPU yields processor control.
Assuming a "modern" operating system the available resources will be shared between processes, therefore if you have 1 application (which is let's say 1 process) that received that 100%, by starting the 2nd application the OS will split that 100% into 50%-50%.