What is a brown dwarf?

1.there no such thing.
2.a star no longer undergoing nuclear fusion.
3.a star right as it undergoes nuclear fusion.
4.an object that is big, but not massive enough to undergo brackets fusion

Water is siphoned from a large tank and discharges into the atmosphere through a 50-mm diameter tube. the end of the tube is b = 2.1 m below the tank bottom which is a = 7.4 m deep, and viscous effects are negligible. determine the maximum height h over which the water can be siphoned without cavitation occurring. atmospheric pressure is 101.4 kpa, and the water vapor pressure is 1.79 kpa (absolute)

Consider a system with two masses that are moving away from each other. why will the kinetic energy differ if the frame of reference is a stationary observer or one of the masses?

Holes drilled several kilometers into earth’s crust provide direct evidence about earth’s interior in the form of