A car travels 1/3 of the distance on a straight road with a velocity of 10 km/hr , next 1/3 with velocity of 20 km/hr and the last 1/3 with velocity of 60 km/hr. what is the average velocity of the car in the whole journey?
Answers
let distance to be covered is 1800.
then time taken for first 1/3 is T
1
=
10
600
=60sec
time taken for second 1/3 is T
1
=
20
600
=30sec
time taken for third 1/3 is T
1
=
60
600
=10sec
total time taken is 100 sec.
av velocity is
100
1800
=18km/s.
Answer:
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Explanation:
Let the total distance travelled be x.
Let the total time taken be T.
Average speed = Total distance/Total time = x/T
First half,
v = 10 km/h
s = 1/3 x
t = (x/3) /10 = x/30
Second half,
v = 20 km/h
s = 1/3 x
t = (x/3) /20 = x/60
Third half,
v = 60 km/h
s = 1/3 x
t = (x/3) /60 = x/180
Now,
Time for entire journey,
T = x/30 + x/60 + x/180
T = 6x + 3x + x/180
T= 10x/180
T = x/18
Now,
Average speed of the entire journey,
Vav = Total distance/Total time
= x/ (x/18)
= 18x / x
= 18 km/h
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