What must occur for an object to be considered a main sequence star?
a. Hydrostatic equilibrium
b. Nuclear fusion reaction in the core
c. Protostar life begins
d. Both a and b
D
You might also like to view...
One angstrom = 
m and one fermi = 
What is the relationship between these units?
A. 1 angstrom = 
fermi
B. 1 angstrom = 
fermi
C. 1 angstrom = 
fermi
D. 1 angstrom = 
fermi
Why are fossils of early life on Earth more rare than fossils of plants and animals from the past few hundred million years?
A) Life was far less abundant prior to a few hundred million years ago. B) Early organisms lacked skeletons and other hard structures that are most likely to be fossilized. C) Fossils could not form before there was oxygen in the atmosphere. D) We find fossils in sedimentary layers, and no sediments were deposited until just a few hundred million years ago.
A roller coaster car (mass = M) is on a track that forms a circular loop (radius = r) in the vertical plane. If the car is to just maintain contact with the track at the top of the loop, what is the minimum value for its speed at that point?
A) rg B) 2rg C) (rg)1/2 D) (2rg)1/2 E) (0.5rg)1/2
A satellite is held in orbit by a 3000-N gravitational force. Each time the satellite completes an orbit of circumference 80,000 km, the work done on it by gravity is:
a. 2.4 × 10^8 J b. 2.4 × 10^11 J c. 9.6 × 10^11 J d. 0