Which of the following statements is true? Efficiency is calculated by multiplying work input and work output.
Only a few machines are 100 percent efficient.
Some machines are frictionless.
The ratio of work output to work input is always less than one.

Air is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. air enters the heat exchanger at 95 kpa and 20°c at a rate of 0.6 m^3/s. the combustion gases (cp = 1.10 kj/kg°c) enter at 160°c at a rate of 0.95 kg/s and leave at 95°c. determine the rate of heat transfer to the air and its outlet temperature.

What is the rate of 12 liters of water moving through a water hose in 4.0 minutes?

An alarm clock has a current of 4.5 amps and a resistance of 3.2 ohms. what is the voltage in the circuit? a.1.4 volts b.0.71 volts c.14 volts d.46 volts