In an emergency, a driver brings a car to stop in 8.0 s. The car was going 21 m/s when the braking began. What was the stopping distance

84 m.

Step-by-step explanation:

Use an equation of motion under constant acceleration:

initial speed u = 21, final speed v = 0, time t = 8, distance s = ?.

s = (u + v) t / 2

= (21 + 0) * 8 / 2

= 168 / 2

= 84 m