An astronaut must journey to a distant planet, which is 211 light-years from earth. what speed will be necessary if the astronaut wishes to age only 15 years during the trip? (give your answer accurater to five decimal places.) hint: the astronaut will be traveling at very close to the speed of light. therefore, approximate the dilated trip time at to be 211 years

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 11.0 m: (a) the initially stationary spelunker is accelerated to a speed of 4.80 m/s; (b) he is then lifted at the constant speed of 4.80 m/s; (c) finally he is decelerated to zero speed. how much work is done on the 78.0 kg rescue by the force lifting him during each stage

Positrons are spontaneously emitted from the nuclei of

Acid precipitation chemically weathering a 5.0-kg limestone rock . which coukd be the result ?