Question

The driver of a car traveling at 54ft/sec suddenly applies the brakes. The position of the car is s=54t-3t^2, t seconds afyer the driver applies the brakes.
How many seconds after the driver applies the brakes does the car come to a stop

Answer 1

  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