When we look at the sun, we are seeing it as it was 8 minutes ago. so we can only see the sun "in the past." when you look at the back of your own hand, do you see it "now" or "in the past"?

What is the rate of 12 liters of water moving through a water hose in 4.0 minutes?

What happens to an isotope during radioactive decay?

Two identical stars with mass m orbit around their center of mass. each orbit is circular and has radius r, so that the two stars are always on opposite sides of the circle. (a) find the gravitational force of one star on the other. (b) find the orbital speed of each star and the period of the orbit. (c) how much energy would be required to separate the two stars to infinity?