Help with Calculus!!

Question

The driver of a car traveling at 60 ft/sec suddenly applies the brakes. The position of the car is s(t) = 60t - 1.5t², t seconds after the driver applies the brakes. How many seconds after the driver applies the brakes does the car come to a stop?

Question options:

1)	60 sec
2)	40 sec
3)	20 sec
4)	10 sec

Answer 1

position of the car is s(t) = 60t - 1.5t², t seconds after the driver applies the brakes. How many seconds after the driver applies the brakes does the car come to a stop?

We need to know when the velocity is zero. velocity is the 1st derivative of distance, so:

v(t) = 60 - 3t

60 - 3t = 0

t = 20