Engineers who design battery-operated devices such as cell phones and mp3 players try to make them as efficient as possible. an engineer tests a cell phone and finds that the batteries supply 10,000 j of energy to make 5500 j of output energy in the form of sound and light for the screen. how efficient is the phone?

At 20∘c, the hole in an aluminum ring is 2.800 cm in diameter. you need to slip this ring over a steel shaft that has a room-temperature diameter of 2.804 cm . 1. to what common temperature should the ring and the shaft be heated so that the ring will just fit onto the shaft? coefficients of linear thermal expansion of steel and aluminum are 12×10−6 k−1 and23×10−6 k−1 respectively.