Question

You are driving home from school steadily at 95 {\rm km/h} for 150 {\rm km}. It then begins to rain and you slow to 50 {\rm km/h}. You arrive home after driving 3 hours and 20 minutes.

(a) How far is your hometown from school?
Express your answer using two significant figures.

(b)What was your average speed?
Express your answer using two significant figures.

Answer 1

(a) Time driving at 95 km/h = distance/speed

= 150/95 = 1.58 h

Time driving at 50 km/h = 3 + 20/60 - 1.58 = 1.75 h

Distance travelled at 50 km/h = speed x time

= 50 x 1.75 = 87.5 km

Total distance travelled = 150 + 87.5 = 237.5 km = 240 km = 2.4 x 10² km

Answer: 240 km or 2.4 x 10² km (2 significant figures)

(b) Average speed = total distance/total time

= 237.5/(1.58 + 1.75) = 71 km/h

Answer: 71 km/h (2 significant figures)