00:01
So in this problem, suppose the core is going towards the positive x direction, and suppose v of t is the velocity of the core at time small t after the brakes were applied at t equals 0.
00:26
So the brakes are applied at t equals 0, let's say, and v of t denotes the velocity at time t.
00:33
And then v0 is given us 60 miles per hour so that's the velocity when the brakes were applied now to keep the units consistent we're going to convert this to feet per second so this becomes 60 times 5 to 80 because one mile is 5 to 80 feet and one out over at 3 ,600 because 3 ,600 because 3 ,000 one hour is 3 ,600 seconds.
01:08
So this is in feet per second.
01:11
And that comes out to be 88 feet per second.
01:15
We also have that the acceleration is given by v prime t equals minus 12.
01:23
And the unit here is feet per second square.
01:26
So the units are now consistent.
01:29
So and the negative sign denotes that it's actually decelerating.
01:36
So the acceleration is negative, the velocity decreases...