a car covers first half of the distance between two places at a speed of 40 km/h and the
second half at 60 km/h. what is the average speed of the car?

If the sun were to become a black hole, what would happen to earth? it is impossible to know the results. it would be sucked in very rapidly. it would continue in the same orbit. it would be sucked in very slowly. 3. which type of radiation us map the galaxy? visible light infrared 21 cm radio waves ultraviolet 4. henrietta leavitt found that the brighter appearing cepheids always had longer periods of light variation. this is an expression of what? period-luminosity relation luminosity function hertzsprung-russell diagram mass-luminosity relation 5. what is the surface or boundary of a black hole called? quasar active galaxy event horizon seyfert point 6. edwin hubble's discovery of a cepheid variable in the andromeda nebula led him to conclude that the nebula was what? a distant galaxy composed of hydrogen a supernova remnant the birthplace of stars 7. earth is near the center of the milky way galaxy. true false 8. how long does it take the sun to revolve around the center of the galaxy? two hundred thousand years two hundred million years two hundred years two hundred billion years