An object slides with friction comes to rest after traveling 80 m. If its acceleration was -4.0 m/s2, what was its initial velocity? Answer= 25m/s I got 320, which is not correct. Please explain Solution From the kinematics equation , V 2 - U 2 = 2*a*S ; where U is the initial velocity, V is the final velocity, a is the acceleration and S is the distance travelled. We are given a = -4 m/s 2 , S = 80 m and since the body came to rest finally, V = 0 m/sec, So the equation is - U 2 = 2*(-4)*80 ==> U 2 = 640 ==> U = (640) 0.5 = sqrt(640) So the inital velocity was U = 25.3 m/sec (Exactly) = 25 m/sec (approximately) .