Question

A girl drove to a hospital from her home and noted that the odometer reading of her car increased by 12.0 km. The trip took 18.0 min
a) what was her average speed?
b) IS she returned home by the same path 7 h 30 min 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 = $\frac{distancetravelled}{time.taken} = \frac{12km}{0.3h} = 40km/h$

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 = $\frac{24km}{7.5h} =3.2km/h$

total displacement = 0 (as starting point and end points are same)
average velocity = total displacement/time = 0

Answer 2

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/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