A person is traveling along a straight road. He moves at a steady 32 m/sec for 6.0 seconds, and then they slow down at a steady rate of 4.0 meters/sec^2 until they come to a stop. (question below)

Question

Their speed was steady from time = 0 sec to time = 6 sec. What was their speed at time = 9 seconds?

I set my equation up like this -4.0 m/s^2 = (v(final) - 32 m/s)/9 s

and I got 4 m/s going backward or -4 m/s. however, my textbook says the answer is 20 m/s.

any help would be much appreciated.

Answer 1

This might help you visualize it better:

Time	Velocity
0 seconds	32m/s
1 second	32m/s
2 seconds	32m/s
3 seconds	32m/s
4 seconds	32m/s
5 seconds	32m/s
6 seconds	32m/s
7 seconds	28m/s
8 seconds	24m/s
9 seconds	20m/s

The equation would be: 32m/s - (4m/s² * (time-6s)) = 32m/s - (4m/s² * (9-6s)) = 20m/s