How do scientist learn about stars and galaxies even tough humans have never been there?

If an electromagnetic wave's frequency doubles in a vacuum, what are the other effects on the wave?

How much work must be done to accelerate an 8.5*10^5 kg train from a) 10m/s to 15m/s b) 15m/s to 20m/s and c) to an Initial stop of 20m/s

A calculus book weighing 20 N rests on the floor of a classroom. The reaction to the force of the floor on the book is a force of

When all the forces on an object are equal and opposite, & the net force is zero, that's ... unbalanced forces. reaction forces. terminal velocity. balanced forces.

A humpback whale took 12.5 minutes to swim 1,170. Meters south at a constant velocity. What was the whale's velocity? __ meters per minute to the south

Which is the correctly balanced equation for the reaction of rust, Fe2O3, and hydrochloric acid, HCl? Fe2O3 + HCl → FeCl3 + H2O Fe2O3 + 3 HCl → 2 FeCl3 + H2O Fe2O3 + 6 HCl → 2 FeCl3 + 3 H2O Fe2O3 + 3 HCl → 2 FeCl3 + 3 H2O

How many DNA strands could you fit into a milimeter

A screwdriver with a 1-cm shaft and a 4-cm handle is used to tighten a screw. calculate the ideal mechanical advantage.

Plants make food through photosynthesis, a chemical reaction. What are the starting substances of the reaction?

How long will it take to travel 200,000 m traveling 100 m/s?