Answer:
8.4 s
Step-by-step explanation:
First of all, let's convert the initial angular velocity of the engine from rpm into rad/s:

The angular velocity at time t is given by:

where
is the angular acceleration, which is negative because the engine is slowing down
We want to know how long it takes for the drive to stop turning: this is equivalent of calculating the time t at which the angular velocity becomes zero,
. Using the equation above, we have:
