What three types of heat transfers involve heat flow to hot object sto colder objects

When the force acting on an object points at least partially in the direction of the motion the work done is considered to be negative

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 man of mass m1 and the woman of mass m2 are standing on opposite ends of the platform of mass m0 which moves with negligible friction and is initially at rest with s = 0. the man and woman begin to approach each other. derive an expression for the displacement s of the platform when the two meet in terms of the displacement x1 of the man relative to the platform.