Hey all, I'm in university right now, though these questions are more geared towards high school. I've completed junior and senior physics in high school, and for some reason I am completely stumped on these two questions. 1. A speeding car passes a highway patrol checkpoint and then accelerates at a constant rate. 4.05 s later, the car is 240 m from the checkpoint and its speed is then 19.7 m/s. What is the acceleration of the car? Since they don't mention V1 (initial) I went ahead and tried the equation [itex] d= v1t + 1/2(a)(t)^2 [/itex] I assumed that V1 was 0, though I don't believe it is since it mentions that the car was speeding when it passed the checkpoint. This left me with (solving for acceleration) [itex] d= 1/2 a(t)^2 [/itex] Which worked out to 29.26 m/s^2. I know this is wrong due to the fact that i need to submit my answer online and it shows that this is an incorrect answer. The next problem i had difficulty with: A ball is thrown straight up from the surface of the earth with and initial speed of 19.2 m/s. Neglecting any effects due to air resistance, what is the magnitude of the ball's displacement (from the starting point) after 0.70 s has elapsed? t = 0.70 s V1 = 19.2 m/s a = -9.8 m/s^2 Therefore I assumed i could easily use [itex] d= v1t + 1/2at^2 [/itex] This works out to 15.84 m, which seems like a resonable answer, though it was wrong. I've also tried entering -15.84, but no luck. Any help you guys can offer is greatly appreciated!