At a speed of 18 km / h, the tractor overcomes a resistance force of 40 kN while it develops power.

We translate the values ​​from given to the SI system:
v = 18 km / h = 5 m / s.
Fc = 40 kN = 40,000 N.
According to Newton’s second law:
The acceleration acquired by the body as a result of the impact on it is directly proportional to the strength of this impact and inversely proportional to the body mass:
F = m * a
In our case, the following forces act on the body:
Ft + Fc = ma, Ft – traction force, Fc – resistance force.
Let’s write in projections on the axis, taking into account that the body moves uniformly:
ОУ: Fт + Fc = 0
Fт = Fc
Power by definition, the ratio of work to time:
N = A / t, and the work is equal to the traction force for displacement A = F * S;
N = F * S / t, taking into account that v = S / t, we get:
N = F * v
Substitute the numbers and determine the cardinality:
N = F * v = 40,000 * 5 = 200,000 W.
Answer: the power developed by the tractor is 200,000 W or 200 kW.