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# When calculating an object’s acceleration that is decelerating to a stop, why does mass not matter even when the forces present depend on it?

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- Andrew SmithLv 71 month ago
You can CALCULATE the acceleration by kinematics which is a form of absolute measurement. You can ESTIMATE OR PREDICT the acceleration using formulae. These may or may not be accurate predictions. For example if you have not correctly allowed for all the frictions involved.

The PREDICTION does involve mass. The MEASUREMENT does not.

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- Anonymous1 month ago
When you push the braking pedal , you generate a braking force BF transmitted to the road through the tires; the effective force EBF can be expressed as the result of the product of the object's weight (m*g) and the the kinetic friction coefficient μk ; in order to avoid skidding, ABS (Anti-lock Braking System) prevents BF > EBF situation .

Since during such motion transient the energy conservation is applied , then :

kinetic energy KE = work W (EBF*distance)

KE = m/2*Vi^2

W = EBF*d = m*g*μk*d

m/2*Vi^2 = m*g*μk*d

mass m cross

braking distance d = Vi^2/(2*g*μk)

since on earth 2g is a costant worth ≅ 20, then :

d = Vi^2/(20*μk)

braking distance is, then, the ratio between the initial squared speed Vi^2 and 20 times the kinetic friction coefficient μk

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- CarolOklaNolaLv 71 month ago
The acceleration of gravity is relative constant is why. It may NOT be exactly 9.817 meters per second squared. That is an average value for Earth. Mass does matter in deceleration, but so does friction and to a certain extent stress (a forces) strain and torque and whether the medium is has or liquid or plasma, pressure(force) and temperature, and the elastic modulae. Of different materials. In basic physics classes you are often told to IG more friction. In basic engineering classes and in reality all of those matter.

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- 1 month ago
Of course its mass matters. Use your hand to apply a force to stop a bike and a train both going 10 mi/hr. Which will take longer to stop? What will have the greater deceleration?

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- skeptikLv 71 month ago
It's not that its mass doesn't matter. It's that you don't need to know it if you already know how its velocity is changing.

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