Angelo is driving at 15.0 m/s when he saw a stalled car 75 m ahead. At what rate must he slow down his car so that it will stop 0.5 m before …
d = 74.5 m
v = Vi + a t
0 = 15 + a t
a t = -15
d = Vi t + (1/2) a t^2
74.5 = 15 t + (1/2) a t^2
74.5 = 15 t + (1/2)(-15) t
74.5 = 7.5 t
t = 9.93 seconds
so
a = -15/9.93 = - 1.51 m/s^2