Hey everyone! i'm new to the forums I just started AP Physics a few days ago and i'm having some trouble on the following problems: 1) A truck on a straight road starts from rest accelerating at 2.0 m/s^2 until it reaches a speed of 20 m/s. Then the truck travels for 20 s at a constant speed until the brakes are applied, stopping the truck in a uniform manner in an additional 5.0 s. (A)How long is the truck in motion? (B)What is the average velocity of the truck for the motion described? ______________________________________________________________ For (A) I found the correct time to be 35 s. For (B), I used the equation: Average velocity = (Vo + V)/2 I set it up like: V = [(0 m/s) + (20 m/s)] / 2 i came up with 10 m/s as my velocity which was wrong. I know this is kind of a multifaceted problem and i'm having trouble adjusting the equation accordingly. Can someone please point out my error and how i can solve this? ______________________________________________________________ 2) A cesna aircraft has a lift-off speed of 120 km/h. (A) What minimum constant acceleration does this require if the aircraft is to be airborne after a takeoff run of 240 m? (B) How long does it take the aircraft to become airborne? _____________ For this problem i used the equation: V^2 = Vo^2 + 2ax I set it up like: (120 km/h)^2 = (0 km/h)^2 + 2(a)(.240 km) i came up with 30,000 km/h^2 which doesn't sound right at all Can someone please point out my error and how i am able to better approach this problem? Help would be very much appreciated thanks! edit: sorry for the vague title, i'll be sure to make it more specific next time.