| Have you ever followed a loaded dump truck in stop-and-go traffic? Not much fun! It's not much fun for Cuthbert, the truck driver either. All those people driving behind honking their horns and, you guessed it, cuthing!
Here's the info for this problem. It takes one full minute for Cuthbert's truck to accelerate from rest to 60 mi/hr but only 10 seconds to bring it back to a halt. As Cuthbert's truck gradually accelerates to highway speed, he tries to remember what he learned in physics about power. Which involves more power: bringing his truck up to speed or stopping it? |
Power is the time rate of doing work or exchanging energy. (If you want power, you have to work overtime! ...get it?)
Since the same amount of work is involved whether speeding up to 60mi/hr or stopping from 60mi/hr, the event which occurs in the smallest time involves the largest power. Therefore, stopping involves more power than speeding up (six times more in this case). The kinetic energy developed during acceleration is converted to heat in the braking mechanism. Keeping brakes cool can be a major problem for trucks carrying large loads downhill! |