Design a system that uses electromagnets to hold open a fire door:

What should the power status of a circuit be when measuring resistance with an ohmmeter?

Which of the following situations is impossible? a) an object has velocity directed east and acceleration directed east. b) an object has zero velocity but non-zero acceleration. c) an object has constant non-zero velocity and changing acceleration. d) an object has velocity directed east and acceleration directed west. e) an object has constant non-zero acceleration and changing velocity.

Name two kinds of practical electric pumps.