In a 60km journey going up hill the upward slop slowed down a car.due to the slowdown, the average speed of car reduce by 15km/h and the time of journey increased by 20 minutes.what is duration of the journey?
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Class 11
>>Physics
>>Motion in a Straight Line
>>Speed and Velocity
>>A car travels up a hill at ...
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A car travels up a hill at a constant speed of 37km/h and returns down the hill at a constant speed of 66km/h. Calculate the average speed for the whole trip.
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Correct option is
A
47.4km/h
The average speed is the ratio of total traveled distance to total time taken.
Let d be the total distance traveled by the car.
Thus distance traveled in each journey is d/2.
So, the time taken for going up the hill is t
1
=
v
1
(d/2)
=
37
d/2
=
74
d
Time taken for going down the hill is t
2
=
66
(d/2)
=
132
d
Thus, average speed is v
avg
=
t
1
+t
2
d
=
(d/74+d/132)
d
=47.4km