An athlete stretches a spring an extra 40.0 cm. how much energy has he transferred to the spring, if the spring constant is 5286.0 n/m?
us= 1/2kx^2 !

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.

Consider a system to be two train cars traveling toward each other. what is the total momentum of the system before the train cars collide?   kg • what must the total momentum of the system be after the train cars collide?   kg •  

In a good thermo flask the main cause of heat loss is