Question

The car has a mass of 1200kg. The car has a forward force of 3400N but friction has a force of 400N going against it. What is the acceleration of the car?

Answer 1

The acceleration of the car : 2.5 m/s²

Further explanation

Newton's 2nd law explains that the acceleration produced by the resultant force on an object is proportional and in line with the resultant force and inversely proportional to the mass of the object  

∑F = m. a  

Mass of the car = 1200 kg

Forward force = 3400 N

Friction force = 400 N

The direction of motion of the friction force will be opposite to the forward force, so that both of them can be subtracted to get the value of the net force (net force: combination / sum of all forces acting on an object)

$\tt \sum F=3400-400=3000~N$

So the acceleration :

$\tt a=\dfrac{\sum F}{m}\\\\a=\dfrac{3000}{1200}\\\\a=2.5~m/s^2$