I'm doing some problems I found here: http://library.thinkquest.org/10796/ch4/ch4q.htm A car is moving at a constant velocity of 20 km/h (5.56 m/s). How much net force is required to raise its velocity to 50 km/h (13.89 m/s) in 30 seconds? Suppose the car has a mass of 150 kg. I used F= (150kg)([13.89m/s-5.56m/s]/30s) and got 41.65 N but apparently that's wrong. What am I doing wrong?