How many times hotter than the sun surface is the surface of a star the same size but gives off twice the amount of energy per second?

The effective temperature of a star is relative to the fourth root of the luminosity and is contrariwise proportional to the square root of the radius. 

L = k R² T⁴ 

If the radius remains continuous, while the luminosity doubles, the temperature must increase by a factor of the fourth root of two. 

If L → 2L, then T → 1.189207115 T

So the answer is approximately 1.19 times.

1) when you rub your hands together quickly, the kinetic energy is converted to mechanical energy.2) thermal energy from the sun travels to earth as infrared waves.3) energy is transferred through the matter of space by electromagnetic waves. 4) when a match is burned, chemical potential energy is converted to thermal and radiant energy. 5) seismicwaves are caused by back and forth movement , or vibration, of an object. 6) mechanicalenergy in an engine changes thermal energy into kinetic energy to make a car move.

It may possibly be c i think |-/