Question

A girl drove to a hospital from her home and noted the odometer reading
of her car increased by 12 km. The trip took 18 minutes. (i) What was her
average speed? (ii) If she returned home by the same path 7h30min after
she left, what was her average speed and velocity for the entire trip?

Answer 1

a) distance travelled by the girl = 12 km

                      time taken = 18 minutes

18 minutes = 18/60 hours

= 0.3 hours

average speed = $\frac{distancetravelled}{time.taken} = \frac{12km}{0.3h}$= 40km upon h

b)

 If she returned home by the same path 7 h 30 min after she left,

total time taken = 7hour and 30 min = 7.5h

total distance travelled = 12+12 = 24 km

average speed = 

total displacement = 0 (as starting point and end points are same)

average velocity = total displacement/time = 0

Answer 2

1. She drove , (Distance ) = 120 Km = 120,000 m

Time = 18 min = 18 x 60 = 1080 seconds

Average speed = total distance /total time = 120,000/1080 = 111.11 m/s = 400 Km/h (better to solve by converting time into hours , calculation would be easier) .

2. return time = 2h 12 min

total time = 2h 12 min + 18 min = 2 h 30 min = 2.5 hours

Return distance = 120 km

total distance = 120 +120 = 240 Km

Average speed = 240 / 2.5 km/h = 96 km/h$.$