How is the mechanical efficiency of a machine usually expressed 1. as a fraction 2. as a percentage 3. as inches or feet 4. as one of three classes

The efficiency of any contraption that uses energy to
do a job is defined as

         (amount of useful energy output) / (amount of energy input) .

In describing or talking about the efficiency f the machine,
it's most often expressed as a percentage.

It's important to notice that the output is taken to be the useful output.
Why is that important ? 
Here's a simple example:

If you use an incandescent light bulb as a source of light, then
the useful output is the light, and its efficiency is quite low.

If you use an incandescent light bulb as a source of heat, then
the useful output is the heat, and its efficiency is quite high.

Answer is c because in exothermic reactions, energy releases.in cellular respiration,atp+h20 (water) = adp+ pi + energyso celullar respiration is exothermic and releases energy

Answer: it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.explanation:   we have equation of motion ,where s is the displacement, a is the acceleration, u is the initial velocity and t is the time taken.average velocity = displacement/ time taken.average velocity = 10.69 miles/hr = 10.69*1.6*1000/(60*60) = 4.75 m/s4.75 = s/ts = 4. 1we also have acceleration = 2.18 m/s², initial velocity = 0 m/sso it will take   4.36 seconds to reach her average velocity 10.69 miles/hour.