Calculating Daily Operating Cost for a Motor at Rated Load

[holy_kamote]

Homework Statement

a motor operates at its rated load of 10 hp for 8.0 h a day. its efficiency is 87 percent. what is the daily cost of operation if electric energy costs 5 cents/kWh?

Homework Equations

The Attempt at a Solution

i convert 10 hp to watts
10 x 746=7460 watts
then i multiply the 7460 with 5 cents and i get 37.3cents/daily cost...
is my answer correct? if not plsss post some idea on how i can solve that ty very much...

 

[holy_kamote]

help me plsssss. coz we will have a boardwork tomorrow ..

 

[PhanthomJay]

You are missing a couple of things. The motor is operating for 8 hours each day...you didn't factor that in. Also, you didn't factor in the efficiency rating. If the motor is rated at 10 hp , that's how much power you get out of it...but more power has to go into it due to the inefficiency losses within the motor, and that's what you pay for.

 

[holy_kamote]

what formula will i use to solve this prob?... thanks sir jay for posting in my topic.

 

[PhanthomJay]

Please show an attempt at a solution. If the motor is 87% efficient, the power into the motor is greater than 10 hp. First calculate that number. Then once you get that power, how would you convert it to energy used (kWh) in 8 hours? We can't be of much more help unless you show some attempt. Thanks.