## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)

We can find the magnitude of the car's deceleration. $F_f = ma$ $mg~\mu_k = ma$ $a = g~\mu_k$ $a = (9.80~m/s^2)(0.50)$ $a = 4.90~m/s^2$ We can use the rate of deceleration to find the initial velocity of the car. $v_f^2 = v_0^2+2ax$ $v_0^2 = 0-2ax$ $v_0 = \sqrt{-(2)(-4.90~m/s^2)(65~m)}$ $v_0 = 25.2~m/s$ The car was traveling at a speed of 25.2 m/s