Which statement about electric and magnetic fields is true

a. electric fields must leave a positive charge and end on a negative charge

b. electric fields and magnetic fields start at a positive and end at a negative.

c. magnetic fields must start at the north pole of a magnet and end at the south pole of a magnet.

d. electric fields loop from south to north

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.