Question

A bucket grain elevator is powered by a 150 kw electric motor. Determine its efficiency if it can lift crain to a height at 60m at a rate of $900m^3/h$. Assume the elevator is lifting wheel with a density of $770kg/m^3$.

• A. 25%
• B. 26%
• C. 51%
• D. 75%

Answer 1

Answer: (D)

75%

$P=\frac{W}{t}=\frac{mgh}{t}=\frac{\rho vgh}{t}$

$P=\rho \frac{v}{t}gh$

$P=770\times \frac{900}{3600}\times 9.8\times 60=113kW$

$\eta =\frac{W_o}{W_{in}}\times 100=\frac{P_o}{P_{in}}\times 100=\frac{113}{150}\times 100=75$%