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Name: Soman P.
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: 2/15/2004


Question:
A truck and a scooter, both are moving in the same direction with same velocity. Which vehicle will come to rest first when the brakes are applied simultaneously?


Replies:
Soman P.,

In an IDEAL situation, provided both vehicles had the same coefficient of friction between wheels and ground, both would stop in the same length of time. If the truck were 1000 times the mass of the scooter, the truck would have 1000 times the momentum and 1000 times the braking force. For constant force, (momentum change)=(force)x(time). The same time works for both situations.

In a REAL situation, the truck takes much longer to stop. This is because the truck's brakes cannot exert enough force to keep the wheels from turning. For a scooter, the brakes freeze the wheels in place. The scooter slides to a halt. For a truck, the brakes only slow the wheels down. There are several reasons for this. First, the force produced by locking the brakes in place would damage both the axles and the wheels enough to be dangerous. Second, the wheels would stop the truck but not the load in the trailer. The material would continue moving forward, crashing into the front panel of the trailer and possibly breaking through. This too would be very dangerous. Large trucks and semis are designed to stop slowly.

Dr. Ken Mellendorf
Physics Professor
Illinois Central College



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