Braking
Approach
Solution
Part B
Approach
The average speed under constant acceleration is (vf + v0)/2. (You can also use stopping distance divided by the time it takes to stop.)
Solution
vave = 19.72/2 m/s = 9.86 m/s
Part C
Approach
Since the braking force results in a constant deceleration, the time it takes to stop can be determined using v = v0 + at.
Solution
Time: t=(v−v0)a=−1972ms−65ms2=303s