A car traveling 75 km/jam slows down at a constant 0,50 m/s2

Question

just by “letting up on the gas.” Calculate (a) the distance the car
coasts before it stops, (b) the time it takes to stop, and (c) the
distance it travels during the first and fifth seconds.

Answer 1

75000 meters/ 3600 seconds = 20.8 meters / second
a = -0.50 meters / second^2
v = Vi + a t
v = 20.8 - 0.50 t
stopped so v = 0
0.50 t = 20.8
t = 41.6 seconds (boring)
d = average speed * 41.6 seconds
= 10.4 * 41.6
= 433 meters (like forever )

during first second
Vi = 20.8
v at 1 s = 20.8 - 0.50 * 1 = 20.3
av v = 41.1/2 = 20.6 m/s
d = 20.6 * 1 = 20.6 meters
during fifth second
v at 4 seconds = 20.8 - 0.50 * 4 = 18.8 m/s
v at 5 seconds = 20.8 - 0.50 * 5 = 18.3 m/s
av v = 18.6 m/s
so in 1 seconds 18.6 meters