Solve the problem.
-The driver of a car traveling at $30 \mathrm { ft } / \mathrm { sec }$ suddenly applies the brakes. The position of the car is $\mathrm { s } = 30 \mathrm { t } - 3 \mathrm { t } ^ { 2 }$, $\mathrm { t }$ seconds after the driver applies the brakes. How many seconds after the driver applies the brakes does the car come to a stop?
A) 15 sec
B) 10 sec
C) 30 sec
D) 5 sec

Question

Quizplus · Accepted Answer

The car comes to a stop when its velocity is 0. The velocity is the derivative of the position function $s(t) = 30t - 3t^2$, which is $s'(t) = 30 - 6t$. Setting this equal to 0 to find when the car stops gives $30 - 6t = 0$, solving for $t$ gives $t = 5$ seconds.

Solve the Problem 30ft/sec30 \mathrm { ft } / \mathrm { sec }30ft/sec

Solve the Problem $30 \mathrm { ft } / \mathrm { sec }$