Question

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?

Answer 1

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.