12. A black hole is

A. an object so diffuse that light leaving it is bent totally back to center of the universe.

B. an object so diffuse that light approaching it is blocked from view.

C. an object so dense that light leaving it is bent totally back to the nearest star.

D. an object so dense that light leaving it is bent totally back to the object.

Acave rescue team lifts an injured spelunker directly upward and out of a sinkhole by means of a motor-driven cable. the lift is performed in three stages, each requiring a vertical distance of 10.0 m: (a) the initially stationary spelunker is accelerated to a speed of 4.90 m/s; (b) he is then lifted at the constant speed of 4.90 m/s; (c) finally he is decelerated to zero speed. how much work is done on the 68.0 kg rescue by the force lifting him during each stage?

Which additional product balances the reaction h2so4 + 2naoh → na2so4 + 2h2o 2oh h2o2 h3o

What sort of waves exhibit the doppler effect?