Question

A lift is reported to operate at 75% efficiency. If the lift can raise a load through a height of 30m using a 230V, 15A supply, calculate how long it will take to raise a load of 1000Kg.

Answer 1

$g = 9.8\frac{m}{s^2}$

$h = 30m$

$m =1000kg$

$\eta=75 \%$

$I = 15A$

$U= 230V$

$\Delta EP = mgh = 9.8*30*1000= 294000\ J$

$W=\Delta EP= 294000\ J$

$\eta =\frac{P_{out}}{P_{inp}}*100\%$

$P_{inp}= IU= 230*15= 3450\ W$

$P_{out}=\frac{P_{inp}\eta}{100\%}=2587.5\ W$

$W =P_{out}t$

$t =\frac{W}{P_{out}}=\frac{294000}{2587.5}=113.62\ s$

$\text{Answer: }t = 113.62\ s$