engineering

Question

Consider the following strange, but true, unit:
 
1 donkeypowerequals=0.33
horsepower [hp]
 
A certain motor is rated to supply an input power of 2500
calories per minute [cal/min] at an efficiency of 90%.
Determine the amount of output power................ donkeypower.(round to 2 sig fig)
 
The output power is...........donkeypowers. (Round your answer to two significant digits.)

Answer 1

Consider the following​ strange, but​ true, unit:
 
1 donkeypowerequals=0.33
horsepower​ [hp]
 
A certain motor is rated to supply an input power of 2500
calories per minute​ [cal/min] at an efficiency of 90​%.
Determine the amount of output power................ donkeypower.(round to 2 sig fig)
 
The output power is...........donkeypowers. ​(Round your answer to two significant​ digits.)

 

Solution:

 

Conversion: 1 HP equals = (641160 cal/hr x hr/60min) =

10586 cal/min

 

The motor has input power of P_in = cal/min at 90% efficiency

 

efficiency ζ = 100% P_out / P_in , ζ P_in = 100% P_out, P_out = ζ P_in / 100%

 

P_out = (90% 2500 cal/min)/100% = 0.9(2500 cal/min)=2250 cal/min

 

HP = 2250 cal/min ( I HP) / 10586 cal/min = 0.21 HP

 

Donkey Power = DP = (0.21 HP x 1 DP / 0.33 HP ) = 0.64 DP