How can astronomers be confident that the larger exoplanets discovered are not simply brown dwarfs?
What will be an ideal response?
Unless the majority of the planets detected are in orbits that we are seeing nearly face on, the objects found are not massive enough to fall into the brown dwarf category. The large number of planets detected by the transit method are in orbits that are nearly edge on, making the minimum mass estimates likely to be fairly close to the actual mass. Many of these have masses much lower than the estimated dividing line between planets and brown dwarfs of about 12 Jupiter masses.
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The formula ?p ? x? h tells us that the product of ?p and ?x cannot be
A) less than h B) greater than h C) equal to h
A 1.0-kg ball is attached to the end of a 2.5-m string to form a pendulum. This pendulum is released from rest with the string horizontal. At the lowest point in its swing when it is moving horizontally, the ball collides elastically with a 2.0-kg block initially at rest on a horizontal frictionless surface. What is the speed of the block just after the collision?
a. 2.3 m/s b. 4.7 m/s c. 3.5 m/s d. 3.0 m/s e. 7.0 m/s
Dielectric mirrors are made to have extremely high reflectance
a. by stacking thin layers of a single dielectric material on a glass backing so that the reflections from the surfaces of the layers undergoconstructive interference. b. by stacking thin layers of a single dielectric material on a glass backing so that the reflections from the surfaces of the layers undergo destructive interference. c. by stacking thin layers of different dielectric materials on a glass backing so that the reflections from the surfaces of the layers undergo constructive interference. d. by stacking thin layers of different dielectric materials on a glass backing so that the reflections from the surfaces of the layers undergo destructive interference.
If the rest wavelength of a certain line is 600 nm, but we observe it at 594 nm, then
A) the source is getting 1% hotter as we watch. B) the source is spinning very rapidly, at 1% of the speed of light. C) the source is receding from us at 10% of the speed of light. D) the source is approaching us at 1% of the speed of light. E) the source is approaching us at 0.1% of the speed of light.