A kettle was tested for its energy efficiency. Its power rating was 900 W. The temperature of 1.0 L of water increased from 24°C to 48°C in a time of 4 minutes and 30 seconds. a. Calculate the energy efficiency of the kettle.
b. Why is the kettle not 100% efficient? What happened to the “missing” energy?

For the car in the picture ,in which direction is the normal force? -into the screen -down -out of the screen -up

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?

The molecular mass of a gas is (select all that apply) a. independent of the type of gas b. the same number as the atomic (or molecular) mass, but measured in grams c. dependent on the temperature d. the mass of a mole of the gas