A computer hard disk starts from rest, then speeds up with an angular acceleration of 250 rad/s2 until it reaches its final angular speed of 7500 rpm. How many revolutions has the disk made 15 s after it starts up?

Consider two less-than-desirable options. in the first you are driving 30 mph and crash head-on into an identical car also going 30 mph. in the second option you are driving 30 mph and crash head-on into a stationary brick wall. in neither case does your car bounce off the thing it hits, and the collision time is the same in both cases. which of these two situations would result in the greatest impact force?