In problems in physics and engineering, answers require units to be meaningful. In designing a quiz question, there should be an option to require that a unit be provided ("3 kg" instead of "3".)  If no unit is provided, or if the unit is incorrect, only partial credit should be given. As a physics professor, I have found that student performance on exams increased dramatically in the area of correctly working with units after I started requiring their homework problems to include units (we were using Moodle, which implements this feature).