In spiral galaxies, the stars orbit around the center faster than predicted. What is the current explanation for this observation

Your target variable is δf, the magnitude of the difference in frequency between the waves emitted from the sonar device and the waves received by the device after reflecting off the whale. write an expression for δf in terms of the relevant frequencies using the subscript notation introduced above.

What will a positive and a negative charge do if they are separated from each other?

What is a possible result of higher air temperature caused by global warming