Horizontal Kinematics - (Acceleration) question?

Question

A driver in a car traveling at a speed of

80 km/h sees a cat 110 m away on the road.

How long will it take for the car to accel-

erate uniformly to a stop in exactly 106 m?

Answer 1

Firstly, the units have to match.  One is in km and the others are in m.  Also, the time will be very short, so it should be converted to seconds (which would be more meaningful than a tiny fraction of an hour)

80km/h

= 80000m/h (multiply by 1000)

=22.22 m/s (divide by 60 for minutes, divide again for seconds)

Average velocity will be the change in velocity ÷ 2

=22.22 / 2

= 11.11m/s

time = displacement ÷ average velocity

t = 106/11.11

= 9.5 seconds