So i answered this question and i got it wrong. the correct answer is in red. can someone explain me why the correct answer is 140s/the temperature starts to rise? i don't understand it.

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?

Mackinzie walks 4 blocks west, then 2 blocks south, then 4 blocks east, and,finally, 1 block south. what is the magnitude of her total displacement duringthis walk (in blocks)?

Suppose the house in question 3 is located in cleveland where the annual average solar flux is 160 w/m2 . if 10 m2 of solar panels operating at 20 percent efficiency were installed on this house to collect and store solar energy in the form of hot water: