When does hydrogen first begin to fuse into helium in the star formation process?
A) when the cloud first begins to contract
B) when the thermal pressure is trapped at the center of the cloud
C) when the protostars undergoes convective contraction
D) when the protostar undergoes radiative contraction
E) only when the star reaches the main-sequence
D
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A squat refrigerator magnet sits on a table with its north pole facing up and its south pole down. We push a ring of wire lying on the table directly toward the magnet. What direction does current flow in the ring when viewed from above? (A wooden table will not affect the magnet’s field.)
A. Clockwise B. Counterclockwise C. No current flows in the loop.
The vibrations of a longitudinal wave move
A) along the direction of wave travel. B) at right angles to the direction of wave travel. C) that changes with speed.
An electric heater is rated 300W 110V. The safety fuse in the circuit can withstand 15 A of current. How many heaters can be safely operated in the circuit?
A) 2 B) 3 C) 4 D) 5 E) more than 5
As you stand by the side of the road, a car approaches you at a constant speed, sounding its horn, and you hear a frequency of 80.0 Hz. After the car goes by, you hear a frequency of 60.0 Hz
What is the speed of the car? The speed of sound in the air is 343 m/s. A) 25.0 m/s B) 64.0 m/s C) 36.0 m/s D) 16.0 m/s E) 49.0 m/s