# Question about acceleration & deceleration in real world?

have searched the net and am not satisfied with any answer I have found to calculate the following:- Here is an example just for reference. Suppose I can accelerate my car from 0-100km/h in 10s. That means my acceleration=2.78m/s/s. Say at 7000Rpm it hits 100km/h in the first gear itself. Now, while I am still very much in gear I lift my leg off the accelerator (no clutch is pressed). It will begin to decelerate, till it hits 1000Rpm and keeps that constant rolling pace of 14km/h. I want to find out the rate at which deceleration takes place? I want you to keep drag/aerodynamics/friction (air & road) etc etc as any normal accepted values, no preciseness required over there. Just need an approximate idea of how I could calculate the rate at which speed drops.

• Why would you down vote a question without even a reason? – user3833732 Dec 29 '15 at 16:40
• Just a note: if you accelerate to 100 km/h in 10 s, your acceleration would be more like 2.78 m/s/s, not 10 m/s/s. – NeutronStar Dec 29 '15 at 16:49
• Only a measurement is going to tell you this. Too many factors like braking on engine, air drag and rolling resistance that are poorly known to make a reasonable estimate, IMHO. – Gert Dec 29 '15 at 16:50
• Sorry @Joshua you are right.. Over sight while trying to exhibit an easy example! ;-) – user3833732 Dec 29 '15 at 18:38
• Yes Gert you are right, but still a car rolling in neutral slows down at a lesser rate than the same car/speed when made to decelerate with still being in gear without the accelerator being pressed. In both cases the forces you have mentioned exists and act upon the same car. But I'm looking at some sort of logic or way of calculating that engine Breaking while the car is still in gear, that makes it slow down faster than the one in neutral, get what i mean? – user3833732 Dec 29 '15 at 19:06