Answer:
after 7 seconds the driver applied the brakes to stop the car.
Step-by-step explanation:
Given:
The position of the car s(t)=[tex]42t-3t^2[/tex]
∴Speed of the car =[tex]\frac{ds}{dt}=\frac{d(42t-3t^2)}{dt}=42-6t[/tex]
When car stopped the speed of car=0
[tex]\Rightarrow42-6t=0\\\Rightarrow6t=42\\\Rightarrow\ t=7[/tex]
Therefore, after 7 seconds the driver applied the brakes to stop the car.
