How to Compute Machine Efficiency?

The efficiency of a machine is the ratio of its output to its input, if both input and output are expressed in the same units of energy or power. This ratio is always less than unity, and it is usually expressed in percent by multiplying the ratio by 100.

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Percent Efficiency = (output energy / input energy) * 100

Percent Efficiency =  (output power / input power) * 100

Also note that 

Input Energy (Power) = output energy (power) + wasted energy (power)

Ang kahusayan ng isang makina ay ang ratio ng output nito sa kanyang input , kung ang parehong input at output ay ipinahayag sa parehong mga yunit ng enerhiya o lakas. Ang ratio na ito ay palaging mas mababa sa isa, at ito ay karaniwang ipinapakita sa porsyento sa pamamagitan ng pagmu-multiply ng ratio ng 100.

Percent Kahusayan = (output enerhiya / input enerhiya) * 100

Percent Efficiency = (output power / input power) * 100

Sample Problems on Efficiency:

1.  A certain light bulb consumes 250J of electrical energy per second, but only emits 35J of light energy per second. Calculate the efficiency of this bulb.

Efficiency = output/input x 100

Output (emits) = 35 joules

Input (consumes) = 250 joules

Efficiency = 55/250 x 100 = 35/250 x 100 = 

0.14 x 100 = 14 or 14%

2. A certain fan is capable of using 4800J of electrical energy each minute, converting 4000J of it into kinetic energy of the fan. What is the efficiency of this fan? 

Efficiency = output energy / input energy

Input energy = 4800 J

Output energy = 4000 J

Efficiency = 4000/4800 = 0.8333 x 100 =  83.33%

3. Jimel's remote-controlled car is 40% efficient, transferring 110J of the total energy into useful kinetic energy. Calculate the total energy input in joules. 

Efficiency = output energy / input energy

Efficiency = 40%

Output energy = 110 J

Input energy = x

40% = 110 / x

0.40 = 110/ x

0.40x = 110

x = 110/0.40

x = 275 J

To check:

Efficiency = 110/275 = 0.40 x 100 = 40%