To calculate the tractive force of the engine, we need to consider the net force acting on the car during its acceleration.
First, we can calculate the acceleration of the car using the given information. The final velocity (v) is 20 m/s, the initial velocity (u) is 0 m/s, and the distance (s) is 80 m. We can use the equation of motion:
v^2 = u^2 + 2as
Substituting the known values:
(20 m/s)^2 = (0 m/s)^2 + 2a(80 m)
400 m^2/s^2 = 160a
a = 400 m^2/s^2 / 160 m = 2.5 m/s^2
The acceleration of the car is 2.5 m/s^2.
Next, we need to consider the forces acting on the car. There are two main forces: the tractive force of the engine (F_trac) and the resistance to motion (F_res). Since the car is accelerating, the net force is given by:
Net force (F_net) = F_trac - F_res
We know that the resistance to motion is 250 N (F_res = 250 N). The net force is also related to mass and acceleration:
Net force (F_net) = mass (m) * acceleration (a)
Substituting the known values:
F_trac - 250 N = 900 kg * 2.5 m/s^2
F_trac - 250 N = 2250 N
F_trac = 2250 N + 250 N
F_trac = 2500 N
Therefore, the tractive force of the engine is 2500 Newtons.