# B So if we used the brake, the accleration would be?

1. Aug 19, 2016

### m0urazz

*Neglect the friction between the car and the earth, but not the friction between the stuff inside the car & the interior surface of the car*
For example, if we're moving with a car at constant speed and we used the brake to stop with constant acceleration, and the stuff inside the car included me had to go forward of course. The question here is, are we going to move forward with the same acceleration that the car stopped with?, if yes can some please one explain it with equation because I got confused if it's about inertia or Newton's third law, if no I hope you clear the idea to me, thanks in advance.

2. Aug 19, 2016

### billy_joule

Firstly, if there is no friction between the car and earth we cannot brake. In fact we cannot even drive at all.

Consider a simpler case - no friction between you and the car:
Draw a free body diagram ( from the reference frame of the earth) and apply Newtons second law - Are there any unbalanced forces on you? So will you accelerate at all?
Now, draw another FBD, this time with friction, you can find an expression for your acceleration in terms on the car's acceleration and the coefficient of friction between you and the car.