Fred has the idea to improve the efficiency of a certain heat engine exploiting a high-temperature reservoir, by using part of its output to run a refrigerator which cools a low-temperature (finite-sized) heat sink to a temperature below the environmental temperature. fiona tells fred that his efforts are futile. who is correct? in particular, what can you say about the overall efficiency of fred's scheme, assuming everything operates reversibly?

Scientists use laser range-finding to measure the distance to the moon with great accuracy. a brief laser pulse is fired at the moon, then the time interval is measured until the "echo" is seen by a telescope. a laser beam spreads out as it travels because it diffracts through a circular exit as it leaves the laser. in order for the reflected light to be bright enough to detect, the laser spot on the moon must be no more than 1.0 km in diameter. staying within this diameter is accomplished by using a special large-diameter laser. part a if λ = 540nm , what is the minimum diameter of the circular opening from which the laser beam emerges? the earth-moon distance is 384,000 km. express your answer to two significant figures and include the appropriate units.

1. a net force of 100 newton’s is applied to a wagon for 5 seconds. this causes the wagon to undergo a change in momentum of

Chemical energy is a form of energy. a. heat b. kinetic c. potential d. electromagnetic