There is no such thing as a formula for deceleration; there is only a formula for acceleration. To find the acceleration, subtract the initial velocity from the final velocity and divide that sum by the time taken. If that formula yields a negative answer, it indicates a negative acceleration, or deceleration.
There are many other formulas related to acceleration in physics. To find the distance traveled, assuming initial velocity, acceleration and time taken are given, the initial velocity can be multiplied by time. That sum can then be added to half of the acceleration multiplied by time squared. There are other more complex formulas that exist, such as the five formulas for constant acceleration. These formulas are designed to describe the motion of a particle that is in a state of constant acceleration.
Deceleration is the rate of decrease of velocity with respect to time. It is the negative of acceleration. The formula for deceleration is the same as that of acceleration, only that
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The formula for it is Deceleration=original velocityfinal velocity)/Time.
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the deaceleration of the formula is same as the normal formula just add on the sign with negative exp F=ma , F = mg if the diretion is opposite the of gravity then is mean decelerate
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Deceleration is nothing but negative acceleration. You can use the formula: S = v²  u²=2as v = final vlocity=0 m/sec u = initial velocity (at the time of applying the brakes
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