What would happen if we used up all the coal on earth?
a. we would make more in a coal factory.
b. more coal would quickly form underneath the earth's surface
c. it would take millions of years to replace. (it would not be able to be replaced in time for us to continue to use.)

The two stars in a certain binary star system move in circular orbits. the first star, alpha, has an orbital speed of 36 km/s. the second star, beta, has an orbital speed of 12 km/s. the orbital period is 137 d. a) what is the mass of the star alpha? b) what is the mass of the star beta?

Sort the images based on whether there's a force of attraction or repulsion between the magnets shown. attraction repulsion

It may seem strange that the selected velocity does not depend on either the mass or the charge of the particle. (for example, would the velocity of a neutral particle be selected by passage through this device? ) the explanation of this is that the mass and the charge control the resolution of the device--particles with the wrong velocity will be accelerated away from the straight line and will not pass through the exit slit. if the acceleration depends strongly on the velocity, then particles with just slightly wrong velocities will feel a substantial transverse acceleration and will not exit the selector. because the acc