A super-insulated house is at a temperature of 20°C. The temperature outside is 0°C. The surface area of the house is 200 m2, and the emissivity is 1 . Approximately how much energy is radiated (in W) per second?
a. 20 000
b. 2 000
c. 200
d. 2
e. 0.2
a
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Algol consist of a 3.7 MSun main-sequence star and a 0.8 MSun subgiant. Why does this seem surprising, at least at first?
A) The two stars should be the same age, so we'd expect the subgiant to be more massive than the main-sequence star. B) The two stars in a binary system should both be at the same stage of life; that is, they should either both be main-sequence stars or both be subgiants. C) It doesn't make sense to find a subgiant in a binary star system. D) A star with a mass of 3.7 MSun is too big to be a main-sequence star.
Which of the following pairs of forces are an action-reaction pair according to Newton’s 3rd law?
A. The push of the road on the car and the push of the car on the road B. The weight of an object and the normal force on the object C. The air resistance on a sky diver and the weight of the sky diver D. The frictional force acting on an object and the force used to push an object
Two identical golf carts move at different speeds. The faster cart has twice the speed and therefore has
A) twice the kinetic energy. B) four times the kinetic energy. C) eight times the kinetic energy. D) none of the above
A magnet of solid metal is placed in a magnetic field. Within the magnet, the magnetic field is greater than that outside (but still oriented in the same direction). The magnet is then heated by an external source to a very high temperature. The magnetic field inside the magnet is now significantly weaker but still greater than the outside field. What kind of magnet is this?