Answers edited by Cosmic Defect

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• What is the difference between hot dark matter and cold dark matter? What difference does it make to cosmology?
  
• If the sun and stars are supported by gas pressure, what supports a white dwarf?
  
• What are spiral nebulae? How did they get their name?
  
• On the WMAP image of the cosmic microwave background radiation, are the higher density irregularities the brighter bits or the darker bits?
  
• Question #27f28
  
• How can we derive Kirchoff's current law and Kirchoff's voltage law?
  
• A room is at a constant temperature of 300 K. A hotplate in the room is at a temperature of 400 K and loses energy by radiation at a rate of P. What is the rate of loss of energy from the hotplate when its temperature is 500 K?
  
• What is the order of the stellar spectral classes?
  
• If the earth were a mile closer to the sun how would it affect our temperature on earth? How far would the earth have to be from it's current orbit to notice a temperature change?
  
• Question #5a7d9
  
• Why don't pendulums work at sea?
  
• As the universe is expanding, is the solar system also expanding?
  
• What is an ellipse?
  
• Is the sun getting bigger?
  
• Question #2f088
  
• What is the average lifespan of a star?
  
• Question #326d7
  
• Question #8db2f
  
• Can someone explain me how this 1.8F came? I know that change in temperature in Celsius scale is equal to change in temperature in Kelvin scale. But, what about Fahrenheit scale?
  
• A person 1.80 m tall stands in front of a plane mirror. What is the minimum height of the mirror, and how high must its lower edge be above the floor for the person to be able to see his/her whole body? Person’s eyes are 6.0 cm below the top of the head.
  
• If the diameter of a circle has endpoints A(7, 2) and B(-1, 8), where is the center of the circle?
  
• Why can’t we determine the distances to galaxies using the geometric method of trigonometric parallax ?
  
• Why is the temperature of the cosmic background radiation not perfectly isotropic?
  
• Question #cd675
  
• Why do metals feel cold even when they are at room temperature?
  
• The half-life of arsenic-81 is 33 seconds. Suppose you have 100 g - how much will remain undecayed after 12.5 days?
  
• Question #01f3b
  
• Question #d496b
  
• How did scientists come up with the Theory of the Big Bang?
  
• Question #0c95e
  
• What torque would have to be applied to a rod with a length of #4 m# and a mass of #2 kg# to change its horizontal spin by a frequency #8 Hz# over #8 s#?
  
• Some very hot rocks have a temperature of #630 ^o C# and a specific heat of #270 J/(Kg*K)#. The rocks are bathed in #45 L# of boiling water. If the heat of the rocks completely vaporizes the water, what is the minimum combined mass of the rocks?
  
• Could I measure the moment of inertia of a fidget spinner by making it the bob of a pendulum? How?
  
• How do I solve this gas problem?
  
• Can the wavelength of light change?
  
• Question #aa702
  
• A tennis ball is thrown from a height #h# above the ground. If the coefficient of restitution #e#, what height will the ball achieve after the third collision ??
  
• Why does the work-energy theory ignores potential energy?
  
• Question #edf16
  
• Poisuille is sI unit of viscosity ? And one pois e is equal to ?
  
• How is it that you can have both water and ice at 0 °C and both water and steam at 100 °C?
  
• Question #2f088
  
• How do you increase the mechanical advantage of a third-class lever?
  
• Does the white dwarf star rotate?
  
• What is the significance of negative sign of electronic energy?
  
• Question #37681
  
• How do you determine if the equation #y=90(5)^x# represents exponential growth or decay?
  
• A copper wire is wrapped 65 times around an unknown core of length 28cm. The current in the wire is 800mA and the magnetic field due to the electromagnet is 1.63 x 10-2T. What is the most likely material the wire is wrapped around?
  
• A #7 L# container holds #12 # mol and #18 # mol of gasses A and B, respectively. Every three of molecules of gas B bind to one molecule of gas A and the reaction changes the temperature from #350^oK# to #175 ^oK#. By how much does the pressure change?
  
• Question #a1b58
  
• A paddle boat can move at a speed of 2 ​km/h in still water. The boat is paddled 6 km downstream in a river in the same time it takes to go 3 km upstream. What is the speed of the​ river?
  
• Question #af0b9
  
• If some galaxies in the local group exhibit blueshift spectral lines, why aren't these blueshifts violations of the Hubble's law?
  
• What is bigger: a globular cluster or a nebula?
  
• How would you calculate the speed at which the moon revolves around the earth in m/s?
  
• Question #b0e5d
  
• What it the current value of the Hubble constant and why is the value so important?
  
• Question #72b9c
  
• What properties of sound waves might determine how loud a sound is?
  
• An object with a mass of #6 kg# is hanging from a spring with a constant of #12 (kg)/s^2#. If the spring is stretched by # 1 m#, what is the net force on the object?
  
• The minimum distance from the origin to the intersection of #x^2+y^2= z# with the plane #x+y+z=12# ?