Answer:
Under assumption that all food energy that needs the horse is transformed into work, then the horse needs approximately 3 megajoules of food energy to work for 1 hour.
Explanation:
Since horse is working steadily, the power experimented by the horse (
), measured in watts, is at constant rate. Then, the work needed by the horse (
), measured in joules, is equal to that power multiplied by time (
), measured in seconds. That is:
(1)
If we know that 
and 
, then the work needed for the horse is:
Under assumption that all food energy that needs the horse is transformed into work, then the horse needs approximately 3 megajoules of food energy to work for 1 hour.
Assuming the earth and the sun to be perfect spheres,
Volume of the sphere = 4/3 * pi * (r**3)
Volume of the earth = 4/3 * pi * ((4000*1.609 km)**3) = 1.116 E 12 km3
Volume of the Sun= 4/3 * pi * ((7 E 5 km)**3) = 1.436 E 18 km3
Density = mass /volume
Density of earth = 6 E 24 kg / 1.116 E 12 km3 = 5.376 E 12 [kg/km3]
Density of Sun= 2 E 30 kg / 1.436 E 18 km3 = 1.392 E 12 [kg/km3]
Density of earth / Density of Sun =
5.376 E 12 [kg/km3] / 1.392 E 12 [kg/km3] = 3.86
The balance chemical reaction is:
<span>6 Li(s) + N2(g) → 2 Li3N(s)
We use the amount of the Lithium reactant and the relations of the substances from the reaction to calculate the amount of product produced. We do as follows:
1.75 mol Li ( 2 mol Li3N / 6 mol Li ) (34.83 g / mol) = 20.32 g Li</span>
