A roller coaster car travels up and down the hills of its track. Neglecting
friction, the sum of its kinetic and potential energy
A. equals the sum of the thermal energy generated by
friction during the ride.
B. is a function of the length of the track.
C. cannot be calculated after the first hill and valley.
D. must always remain constant.

option D is the correct option

Must always remain constant

Explanation:

According to their law of conservation of energy :it states that in a closed system,the total mechanical energy is always constant although energy may change from one form to another. e. g from potential energy to kinetic energy

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:

grav forces affect all objects magnetic forces affect magnetic objects and electric currents