3. Consider an infinite long wire with a linear mass density p. If r denotes the distance from the wire, (a) find the gravitation field as a function of r. (5 pts) (b) find the gravitation potential as a function of r (you could leave a constant free parameter in the result). (5 pts) (c) For a particle of mass m released from rest at r=ro, what is the speed of the particle when reaching r=ro/2. (5 pts)