For a star like the Sun, the gravitational collapse of the interstellar cloud lasted for about ________ and stopped with the ignition of the fusion reaction.
A. 1-10 million years
B. 100 million years
C. 5-10 billion years
D. 1 billion years
E. 50-100 billion years
Answer: A
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A neon light (thin hot neon gas in a sealed tube) gives us
A) a continuous spectrum, since the neon is hot enough to glow. B) a few bright emission lines, telling us the gas is neon. C) a continuum, with dark lines identifying the neon atoms that are present. D) a lot of random bright red lines due to the motion of the hot atoms. E) nothing visible to us, but a lot of infrared lines as heat.
In a dream you're in a car traveling at 50 km/h and you bump into another car traveling toward you at 48 km/h. The speed of impact is
A) 48 km/h. B) 50 km/h. C) 98 km/h. D) 2400 km/h.
The Aswan High Dam on the Nile River in Egypt is 111 m high. What is the gauge pressure in the water at the foot of the dam? The density of water is 1000 kg/m3
A) 1.11 × 102 Pa B) 1.09 × 106 Pa C) 1.11 × 105 Pa D) 1.09 × 103 Pa E) 1.16 × 106 Pa
What is the ionosphere?
A) a layer of the atmosphere that is above the exosphere B) a layer of the atmosphere characterized by the presence of ozone C) a portion of the thermosphere in which the gas is ionized D) a portion of the troposphere in which ions are common