One of the main reference lines on the spectrum of hydrogen is located at 650 nanometers. if the placement of this line on the hydrogen spectrum from a distant star was at 649 nanometers, this would indicate that
the star has no radial motion with respect to earth
the star is moving toward earth
the star is moving away from earth

An astronaut in space cannot use a scale or balance to weigh objects because there is no gravity. but she does have devices to measure distance and time accurately. she knows her own mass is 77.4 kg , but she is unsure of the mass of a large gas canister in the airless rocket. when this canister is approaching her at 3.50 m/s , she pushes against it, which slows it down to 1.30 m/s (but does not reverse it) and gives her a speed of 2.60 m/s . what is the mass of the canister?