Help please, it’s on my physics paper!

Find the magnetic field a distance r from the center of a long wire that has radius a and carries a uniform current per unit area j in the positive z direction.

The california mussel (mytilus californianus) attaches itself to a rock or other solid surface with a bundle of filaments known as the byssus. imagine that 15.0 j of work is done to stretch the distal end of the byssus. it releases 10.8 j of thermal energy as it relaxes. what is the resilience of the distal end of the byssus?

Acoil suspended freely, points in some direction when no current is passed through it . can you tell what will happen when a current is passed though it?