Un coche que viaja a una velocidad de 30m / s, frena y desacelera a 2m / s ^ 2 hasta detenerse?

Propongo esta solución :

Recordemos.

Dos ecuaciones básicas de la cinemática :

<img src="https://tex.z-dn.net/?f=v_%7Bf%7D%3Dv_%7Bi%7D%2Bat%5C%5Cd%3D%5Cfrac%7B1%7D%7B2%7D%28v_%7Bf%7D%2Bv_%7Bi%7D%29t%5C%2C%5Ctextup%7BDespejando%20t%2Cen%20la%20primera%20ecuaci%5C%27on%20y%20tomando%20en%20cuanta%20que%20vf%3D0%20se%20tiene%3A%7D%5C%5Ct%3D%5Cfrac%7Bv_%7Bf%7D-v_%7Bi%7D%7D%7Ba%7D%5C%2C%5Ctextup%7BSustituyendo%20en%20la%20segunda%20ecuaci%5C%27on%2Cnos%20queda%3A%7D%5C%5Cd%3D%5Cfrac%7B1%7D%7B2%7D%28v_%7Bf%7D-v_%7Bi%7D%29t%3D%5Cfrac%7B1%7D%7B2%7D%28v_%7Bf%7D-v_%7Bi%7D%29%28%5Cfrac%7Bv_%7Bf%7D-v_%7Bi%7D%7D%7Ba%7D%29%5C%2C%5Ctextup%7Bpero%7D%5C%5Cv_%7Bf%7D%3D0%5CRightarrow%20d%3D%5Cfrac%7B1%7D%7B2%7D%280-v_%7Bi%7D%29%28-%5Cfrac%7Bv_%7Bi%7D%7D%7Ba%7D%29%5C%2C%5Ctextup%7BSustituyendo%20los%20valores%20previos%20se%20tiene%3A%7D%5C%5Cd%3D%5Cfrac%7B1%7D%7B2%7D%280-30%5C%2Cm%2Fs%29%28-%5Cfrac%7B30%5C%2Cm%2Fs%7D%7B2%5C%2Cm%2Fs%5E%7B2%7D%7D%29%5C%5Cd%3D%5Cfrac%7B1%7D%7B2%7D%28%5Cfrac%7B900%5C%2Cm%5E%7B2%7D%2Fs%5E%7B2%7D%7D%7B2%5C%2Cm%2Fs%5E%7B2%7D%7D%29%5C%5Cd%3D%5Cfrac%7B900%5C%2Cm%5E%7B2%7D%2Fs%5E%7B2%7D%7D%7B4%5C%2Cm%2Fs%5E%7B2%7D%7D%5C%5Cd%3D225%5C%2Cm" />

Saludos.