How can someone calculate the stopping distance of their car?


Quick Answer

The stopping, or braking, distance of a car is twice the original speed divided by the value of twice acceleration due to gravity, multiplied by the sum of the surface grade and the friction between the tires and the road. Braking distance is dependent upon speed and the roadway, so it varies in different situations.

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Full Answer

Stopping distance is the time necessary for a vehicle to stop completely after braking. A few variables affect stopping distance, making it variable in different situations. Stopping distance is shorter on an uphill slope and longer on a downhill. This variable is the grade of the surface.

Friction is another important consideration. Worn tires or a wet surface increase stopping distance. Finally, the original speed of the vehicle impacts stopping distance, as a faster vehicle requires a longer distance to come to a complete stop.

Stopping distance also depends on one constant value, the acceleration due to gravity, which is 32.2 feet per second squared in every situation. When calculating stopping distance, the surface grade is reported as a percentage in decimal units. For example, a 5 percent grade would be .05 in the calculation.

The calculation for stopping distance is written as d = 2V/[2g(f + G)]. In this equation, d is the stopping distance, V is the original speed, g is acceleration from gravity, f is friction and G is the surface grade.

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