George is driving 100 ft/sec toward an intersection.
He looks to his right, and sees Bill, driving 30 ft/sec toward the same intersection. George foolishly slams on his brakes.

If he had kept going 100 ft/sec, he would have been through the intersection long before Bill got there.

At the instant that he slams on his brakes, the center of George's car is 125 ft from the intersection, and the center of Bill's car is 150 ft from the intersection. George's brakes give his car an acceleration of -30 ft/sec².
Bill never changes his speed.
Each car is 13 ft long and 7 ft wide.

Will there be a collision?

(In reply to Solution by Hot Date Dave)

No David.

As Charlie has already pointed out (and as I'm guessing that DJ was trying to show by proposing the problem), you are simply blindly applying the equations.

The equation shows a CONSTANT -30 ft/sec/sec. But that's not what happens. When the car finally stops... the brakes don't "push" the car backwards... The car will stop in less than 5 seconds (past the intersection). If the car then continued with a -30 ft/sec/sec acceleration, it would back up into the intersection and collide. But it doesn't.

So, Charlie was correct in that there is no collision.

Posted by SilverKnight on 2003-10-02 13:00:45