Why is an iron core needed in an electromagnet?

Edward tolman explained the results of his study by theorizing that the rats were learning about the maze during every trial but they a. were agitated because other groups were getting reinforcement b. could not remember how to demonstrate it without reinforcement c. were not motivated to demonstrate it without reinforcement d. seemed to be too lazy to actually work without reinforcement

Waves that cause the most damage during an earthquake are a. surface waves c. s waves b. p waves d. ocean waves

What properties of a moving object are used in determining the object's energy of motion