A book starts on a shelf 1 m off of the ground. You then move the book to a higher shelf that is 3 m off of the ground. If the system gained 20 J of gravitational potential energy, what is the mass of the book?

Two 1.20-m nonconducting wires meet at a right angle. one segment carries + 2.50 µc of charge distributed uniformly along its length, and the other carries - 2.50 µc distributed uniformly along it, as shown in fig. 21.50. ( a. find the magnitude and direction of the electric field these wires produce at point p, which is 60.0 cm from each wire. ( b. if an electron is released at p, what are the magnitude and direction of the net force that these wires exert on it?