Question

an object moving at 30 m/s takes 5s to come to a stop. what is the object's acceleration?
A. 30 m/s ^2
B. -30 m/s ^2
C. -6 m/s ^2
D. 6 m/s ^2

Answer 1

use SUVAT where:
S = distance
U = initial velocity = 30m/s
V = end velocity = 0 m/s
A = acceleration = ?
T = time = 5 secs

then pick out the equation v = u + at

so:
0 = 30 + 5a
-30 / 5 = a
a = -6 m/s^2