Which of the following statements correctly describes the models put forth by ptolemy and copernicus to explain the universe? a. the model developed by copernicus was simpler and had less inconsistencies than ptolemy’s model. b. the sun was in the center of ptolemy's model, but the earth was in the center of copernicus' model. c. through observations, both astronomers presented models where the earth remained stationary. d. both of the models were easy to understand and thus were well received by the public almost instantly.

Space-time metric ds2= -dt2+at2dx2+bt2dy2+ct2dz2 (a)how does the area of a rectangle with vertices at ( x=0, y=0, z=0 ), (1,0,0 ), ( 0,1,0 ) and (1,1,0 ) changes with time? (b) if a photon moving in the x direction starts from the origin at t=1, when does it reach x=l? (ds=0 for the trajectory of a photon.) (c) the proper time for a particle is defined by cd=ds. what is the proper time for a particle to move along the trajectory ( x(t)=t, y(t)=0, z(t)=0 ) from t=0 to 1 ? what is the condition on the parameter a so that the velocity of the particle never exceeds the speed of light ?

Frost wedging occurs when water seeps into a crack in a rock, freezes, and causes the crack in the rock to widen. t or f

11. you want to calculate the displacement of an object thrown over a bridge. using -10 m/s2 for acceleration due to gravity, what would be the total displacement of the object if it took 8 seconds before hitting the water?