| Arnold was
driving down US 41.5 in his 1999 Whizzer when he spotted a strange object
in the sky. "Gee," said Arnold, "If I were the first to greet these aliens,
I'd be famous!" Unfortunately, Arnold should have been thinking more about
his driving, because his 3000-kg car, which was traveling at 20 m/s, slammed
into a telephone pole. The distance it took for the car to stop was only
3 meters.
Let's see if you know the meaning of work! What was the magnitude of the average force that stopped Arnold (and his car)? |
The easiest solution uses the fact
that work done equals change in energy.
Arnold and car had (0.5)mv2 units of K.E. to lose. Work is Fd. So, KE = (0.5)(3000 kg)(20 m/s)2 = 6 x 105 Joules. F = (change in KE) / (displacement) = 6 x 105 Joules / 3 m = 2 x 105 N. I hope Arnold was wearing his seatbelt! |