A550 kg car accelerates from 15 m/s to 25 m/s in 15 s by applying a constant force. how large of a force is exerted? show work

You'll be using the equation f = m a, or force = mass x acceleration

First, you have to find the acceleration. The acceleration needed is the average acceleration over the 15 seconds is accelerated. So, you take the change in speed (25m/s - 15m/s) to get a change of 10m/s. 
The average acceleration (acceleration per second) is found by dividing total acceleration by the time it took. So, it's 10 / 15, which equals .6. This is a, your acceleration
Now just plug it into the equation F = m a, because it already gives you the mass of the car
F = 550 x .6
Solve that to get F = 366.6. F is measured in Newtons (N), so your answer is 366.6N

The actual answer is c force stays the same while direction changes