Which is brighter in our sky, a star with apparent magnitude 2 or a star with apparent magnitude 7? How many times brighter does it appear?
What will be an ideal response?
A star with apparent magnitude 2 is 100 times brighter than a star with apparent magnitude 7. (Larger apparent magnitude stars are always fainter.)
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Conduction: The thermal conductivity of a certain concrete is 0.80 W/m . K and the thermal conductivity of a certain wood is 0.10 W/m ? K. How thick would a solid concrete wall have to be in order to have the same rate of heat flow through it as an 8.0-cm thick wall made of solid wood? Both walls have the same surface area and the same temperature difference across their faces.
A. 53 cm B. 64 cm C. 71 cm D. 85 cm
An ice skater has a moment of inertia of 5.0 kg ? m2 when her arms are outstretched, and at this time she is spinning at 3.0 rev/s
If she pulls in her arms and decreases her moment of inertia to 2.0 kg ? m2, how fast will she be spinning? A) 2.0 rev/s B) 3.3 rev/s C) 7.5 rev/s D) 10 rev/s
You throw a ball up in the air and hold your hand under it to catch it when it comes down. The reason why the ball stops is because
a. your hand is there: your hand exerts no force on the ball. b. your hand exerts a force on the ball perpendicular to its velocity. c. your hand exerts a force on the ball in the direction of its velocity. d. your hand exerts a force on the ball in the direction opposite to its velocity. e. your hand and the ball exert forces in the same direction on each other.
According to the law of reflection, a light ray striking a mirror at an angle of incidence of 30 degrees will leaves the mirror at an angle of
a. 60 degrees b. 30 degrees c. less than 30 degrees d. none of the above