physics
posted by julie on .
A small motor draws a current of 1.76 A from a 110 V line. The output power of the motor is 0.20 hp.
(a) At a rate of $0.060/kWh, what is the cost, in cents, of operating the motor for 4.0 h?
(b) What is the efficiency of the motor?
for (a) i am doing IV*hours*price and its coming up worng.
and for (b) i changed .2hp into Watts. and i got 149.2W.
im just not sure how to do this problem.

Pin=VI=110 * 1.76=193.6W = 0.1936KW.
a. C = $0.060/kwh * 0.1936kw * 4h =
$0.0465 = 4.65 cents.
b. Po = 0.2hp * 746W/hp = 149.2W.
%Eff.=(Po/Pin)100%,
%Eff.=(149.2/193.6)100% = 77.1