20. consider two stars a and b with temperatures ta and tb and radii ra and rb respectively. if ta
= 2 tb and ra= 12 rb, which statement about the stars' luminosities, la and lb, is true?
using this formula: l=(r^2)(t^4)
a) la =lb
b) la = 2 lb
la=4 lb
d) la = 12 lb
e) la = 14 lb

Why do electron microscopes have higher resolving power than light microscopes?

Aprojectile is launched from ground level with an initial velocity of v 0 feet per second. neglecting air resistance, its height in feet t seconds after launch is given by s equals negative 16 t squared plus v 0 t. find the time(s) that the projectile will (a) reach a height of 192 ft and (b) return to the ground when v 0equals112 feet per second. (a) find the time(s) that the projectile will reach a height of 192 ft when v 0equals112 feet per second. select the correct choice below and, if necessary, fill in the answer box to complete your choice.

Need people build a dam to create a reservoir that supplies water a nearby city needs. describe two ways this action will likely affect the water cycle in the local environment. (5 points) worth 20 points