Your 1996 civic99civic engine shakes violently only during acceleration and stops when not your rear mount has found to be cracked could it that simple?

Yes, a cracked rear engine mount in a 1996 Honda Civic could absolutely cause violent shaking during acceleration. The engine mounts are designed to isolate the engine from the chassis, and a cracked rear mount would allow excessive engine movement, especially under the stress of acceleration. This movement translates into the shaking you're experiencing. Since the shaking stops when you're not accelerating, it strongly points to the rear mount as a likely culprit.