The driver of a car traveling at 60 ftsec suddenly applies t

The driver of a car traveling at 60 ft/sec suddenly applies the brakes. The position of the car is s = 60t - 3t2, t seconds after the driver applies the brakes. How many seconds after the driver applies the brakes does the car come to a stop?

s = 60t - 3t^2 v = ds/dt = 60 - 6t when it comes to rest, v = 0, so t = 10 sec now distance travelled = time taken x average velocity = 10 x (60 + 0)/2 = 300 ft