Assuming a 25% efficiency, how many Calories would a horse need to consume to work at 1.0 hp for 2.0 hh ?

E = 7.11 ×  Cal

Explanation:

given data

efficiency = 25 %

solution

first we get here E by the power that is express as

p =     ...........1

E = p × t

E = 1 ×  2 ×  

E = 7.447 × J

and

Ein is get by efficiency

Ein =        ..................2

Ein =

Ein = 29.788 ×  J

so required energy is

E = 29.788 ×  ×  

E = 7.11 ×  Cal

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)