# Braking Distance

Here is some braking-distance
data. You might want to compare the following solution with the
work-energy
approach.

##

A Solution:

### Average velocity:

If the truck starts with twice the velocity, its** average
velocity will be twice as much** as before, since:

average velocity = (starting velocity + ending
velocity)/2

### Time:

Newton's Second Law says:

acceleration of the truck = (net force on the truck) /
(truck's mass)

Assuming that the brakes are applied with maximum force each time,
the net force on the car due to its brakes will be the same each
time. The mass of the truck will stay the same - therefore the
**acceleration of the truck will be the same** in each case.
Now:

acceleration = (change in velocity) / time

Since the change in velocity will be twice as much when the truck
is initially going twice as fast, **the time to stop the truck must
double** in order that the acceleration is the same.

### Distance:

The distance the truck travels is given by:

distance = (average velocity)(time)

Since both the average velocity of the truck and the time to stop
double, **the distance to stop the truck will be
****four times**** as much (48
meters**) when the truck's velocity doubles.

last update December 26, 2005 by JL
Stanbrough