Find the current to run an electrical motor that has an output of 2.1 horsepower and is 71% efficient. operates at 171 volts answer to nearest tenth of an amp.

Wow!

1 horsepower = 746 watts

2.1 horsepower = (2.1 x 746) = 1,566.6 watts

Since the motor is 71% efficient, 1,566.6 watts = 71% of the input power.

1,566.6 = 0.71 P

Divide each side by 0.71 : input Power = (1,566.6 / 0.71) watts

(Let's leave it like that for right now. The final answer will be more accurate

if we can avoid rounding until the very end.)

Input power = (voltage) x (current)

(1,566.6/0.71 watts) = (171 volts) x (Current)

Divide each side by 171 volts: Current = (1,566.6) / (0.71 x 171) = 12.903 Amps.

Current = 12.9 Amperes.

Check:

(volts x Amps) x (efficiency) = output power

(171 x 12.9) (watts) x (71%) x (1 HP / 746 watts) =

(171 x 12.9 x 0.71) / (746) HP = 2.0994 HP

Close enough to 2.1 for Engineers!

yay!