Which part of a refrigerator determines whether it is an open or close system? how can you change the system from close to open

An incident ray through the focal point of a spherical mirror will: reflect through the center of curvature. reflect back through the focal point. reflect parallel to the principle axis. reflect the same direction as the incident ray.

Aria drove to the store, did some shopping, and then came home. during maria's trip, when was her displacement equal to zero?

Which are true about beta reactions? there will be more than one answer. a. it has no change b. it doesn't change the mass of the number c. it has a mass of 0.0005 atoms d. it causes transmutation.