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?

efficiency= [useful energy transferred ÷ total energy supply]×100%

So, [5500÷10000]×100%=0.55×100

                                        =55%

answer: the exterior temperature of commercial jet planes as they leave the stratosphere and return to the ground increases steadily.

explanation:

the lower most layer of atmosphere is troposphere which extends from 0 to 12 km above the surface of the earth. the temperature initially decreases as distance is increased from the earth's surface. commercial jets fly in lower part of the stratosphere. the stratosphere extends upto 50 km. the temperature in stratosphere starts rising again due to presence of ozone which traps the uv rays.

thus, when the planes leave the stratosphere and return to the ground, the exterior temperature increases steadily.

prolly a beacuse the momentuem the car has increases while going down hill