A wagon is pulled at a speed of 0.40 meters/sec by a horse exerting an 1,800-newton horizontal force. what is the power of this horse?

The answer is: 720W

The definition of Power is:P = L/t = →F⋅→s/t = →F⋅→s/t = →F⋅→v

The ⋅ in the last formulation designate a scalar product, well-defined by:

→v. →w = |v| |w| cos (ˆvw), the angle ˆvw is 0 because →F and →v are parallel, so the cosinus is 1.

So: P=1800N⋅ 0,40m/s=720W.