1. A 40 kg rock falls from rest from the top of a 64 m high tower and falls with negligible air resistance. How much kinetic energy (KE) and potential energy (PE) does the rock have when it is 28 m above the ground?
(A) KE = 0; PE = 2.5 x 104

J (B) KE = 1.1 x 104 J; PE = 1.4 x 104

J (C) KE = 1.4 x 104 J; PE = 1.1 x 104

J (D) KE = 2.5 x 104 J; PE = 0

a solenoid is created by wrapping a l = 90 m long wire around a hollow tube of diameter d = 4.5 cm.   the wire diameter is d = 0.9 mm.   the solenoid wire is then connected to a power supply so that a current of i = 9 a flows through the wire.

randomized variablesl = 90 m

d = 4.5 cm

d = 0.9 mm

i = 9 a                                          

write an expression for the number of turns, n, in the solenoid. you do not need to take into account the diameter of the wire in this calculation.

calculate the number of turns, n, in the solenoid.

write an expression for the length of the solenoid (l2) in terms of the diameter of the hollow tube d.

calculate the length of the solenoid (l2)   in meters.

calculate the magnitude of the magnetic field at the center of the solenoid in teslas.

explanation:

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.