Question 1208332
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The car's speed decreased linearly as a function of time. 
The speed was 60 kph at t=1s and 40 kph at t = 5 s. 
Create a function that describes speed as a function of time. At what time did the car's speed equal 0?
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<pre>
The function is  

    f(t) = V - at,    (1)


where V is the initial speed at t= 0, "a" is the rate of the speed decreasing, t is the time (in seconds).


We don't know V at t= 0  (it is not given),  but we can easily find "a".



"a" is the ratio of the change of the speed to the elapsed time

    a = {{{(60-40)/(5-1)}}} = {{{20/4}}} = 5 kilometer per hour per second.



Now from equation (1) we will find V

    V - 5*1 = 60 ,

    V = 60 + 5 = 65.


Thus the function is  f(t) = 65 - 5t kilometers per hour.    <U>ANSWER</U>



To find the stop time, write this equation

    V = 65 - 5t = 0.


From the equation,  t = 65/5 = 13 seconds from the beginning.    <U>ANSWER</U>
</pre>

Solved, with all necessary explanations.