A car travels from point A to B in 3 hours and returns back to point Ain 5 hours, Point A and B are 150 km apart
along a straight highway. What is the average speed of the car in this journey?
a) 18.75 km/h
b) 375 km/h
c) 30 km/hr
d) 50 km/hr
Answers
ANSWER
Time taken to travel distance S
t1=V1S=30S......(1)
t2=V2S=50S……(2)
Average speed=totaltimeTotaldistance=t1+t2S+S=30S+50SS+S
Average speed=30+50100×30=37.5kmh−1
Since Initial and final position are same displacement is zero.
The average speed of car in the journey is 37.5 km/h. hence option (b) 37.5 km/h is correct choice.
A car travels from point A to B in 3 hours and returns back to point A in 5 hours, Point A and B are 150 km apart along a straight highway.
We have to find the average speed of the car in this journey.
method 1 : Distance between A and B is 150 km
average speed = total distance/total time taken
= (150 km + 150 km)/(3 hrs + 5 hrs)
= 300/8 km/h
= 37.5 km/h
Therefore the average speed of car in the journey is 37.5 km/h.
method 2 : speed of car from A to B , v₁ = distance covered/time taken
= 150km/3 hrs = 50 km/h
speed of car from B to A , v₂ = distance covered/time taken
= 150 km/5 hrs = 30 km/h
using formula,
average speed , Vav = 2v₁v₂/(v₁ + v₂)
[ this formula is applicable only when body moves same distance with different speeds ]
= (2 × 50 × 30)/(50 + 30)
= 3000/80
= 300/8
= 37.5 km/h