rasen58 Posted December 25, 2014 Share Posted December 25, 2014 A car accelerates uniformly from rest, covering a distance of 125 m in 5 s. What is the car's acceleration in m/s^2? I thought the velocity would just be d/t = 125/5 = 25 m/s And then I thought the acceleration would be v/t = 25/5 = 5 m/s^2 But apparently the answer is 10 m/s^2 Why? Link to comment Share on other sites More sharing options...
Behrus58 Posted December 25, 2014 Share Posted December 25, 2014 Hi. You can't use d/t for a movement that has acceleration.do you want to find the velocity of the start of the movement ? you don't need that. From v=at+v0 , we know that : x = 1/2 (a)(t)^2 + (v0)(t) + x0 so just put these numbers : x = 125 , t = 5 and you'll have a = 10 m/s^s The reason you can't use d/t is that , the idea v = d/t is only for movements with no acceleration , which have a constant velocity. Link to comment Share on other sites More sharing options...
rasen58 Posted December 26, 2014 Author Share Posted December 26, 2014 Oh wow, I didn't know that. Thanks, that helps. Link to comment Share on other sites More sharing options...
swansont Posted December 26, 2014 Share Posted December 26, 2014 A car accelerates uniformly from rest, covering a distance of 125 m in 5 s. What is the car's acceleration in m/s^2? I thought the velocity would just be d/t = 125/5 = 25 m/s That would be the average velocity, but the final velocity has to be higher. Since a is constant and you start from v=0, the final speed is actually twice the average. Link to comment Share on other sites More sharing options...
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