What are the approximate spectral classes of stars with the following characteristics?
balmer lines of hydrogen are very strong; some lines of ionized metals are present.
the strongest lines are those of ionized helium.
lines of ionized calcium are the strongest in the spectrum; hydrogen lines show only moderate strength; lines of neutral and metals are present.
the strongest lines are those of neutral metals and bands of titanium oxide.

A47 kg person in a rollercoaster moving through the bottom of a curved track of radius 47.7 m feels a normal force of 895 n. what is the net centripedal force acting on the person

No matter what energy transformation we discuss, we know that no energy transfer is 100% efficient. you are about to enter a bicycle rave. you have trained extensively and eaten well to maximize your energy input throughout the bicycle race. you know that some of your kinetic energy will become wasted energy in the form of heat. what is the source of the heat energy and how can you minimize it to maximize the efficiency of your performance in the race? a) you are the source of the heat energy. you can minimize the heat energy but selecting the appropriate clothes to wear. b) air resistance is the source of he heat energy. you can minimize the air resistance by your position while riding the bicycle. c) friction is the source of the heat energy. you can minimize the friction by lubricating all appropriate parts and keeping the tires well inflated. d) kinetic energy is the source of the heat energy. you can reduce the production of heat energy but minimizing the energy you expend to race on the bicycle.

If 50 ml of each of the liquids in the answer choices were poured into a 250 ml beaker, which layer would be directly above a small rubber ball with a density of 0.960 g/ml? a. sea water – density of 1.024 g/ml b. mineral oil – density of 0.910 g/ml c. distilled water – density of 1.0 g/ml d. petroleum oil – density of 0.820 g/ml