THERMO Spoken Here! ~ J. Pohl ©  ( C0850~2/15)( C1000 -  Clean Garage)

Bounce of a Brick

p A son with his date is driving his father's Mercedes, safely, at 50 miles per hour but maybe a bit close behind a truck loaded with bricks. Placing her hand on his arm, his date says, "Ohh Honey, is a brick falling off that truck?"

The sketch shows the scenario.

Is there any chance the brick might bounce over Dad's Mercedes?
♦  This will be a "batch" event that starts the moment the brick falls from the truck and ends at the greatest height it might attain finally - assuming a "perfect" bounce. For the brick taken as a BODY energy equation is:

(1)1

For the "bounce event" the second possible elevation will be greatest when there is no work. So we assume "no work." Thus:

(2)2

Wow! Our calculations predict the brick might bounce upward 90 feet. So there should be no problem for Dad's car... Right?

Our calculations assumed energy of the brick to be conserved. We know that won't happen. However, our calculations are correct - subject to our assumptions.

Although initial calculations require assumptions, their answers are not useless. With assumption our answers become a "bound" for reality. So what can his date say to this Dude with certainty?

Honey, the brick might bounce, but no higher than 91.5 feet!

Perfect Bounce

A son who borrowed his father's Mercedes is driving safely at 50 miles per hour but bit too closely behind a truck loaded with bricks. His date says,

"Honey, is a brick falling off that truck?"

Is there any chance the brick might bounce over Dad's Mercedes?