4. A train moving with a velocity of 30 km.p.h has to slow down to 15 km.p.h.due to
repairs along the track. If the distance covered during retardation be one kilometer and
that covered during acceleration be half a kilometer,find the time lost in the journey.
Answers
Answer:
Explanation:
The whole solution is in the pics.
Answer:
The time lost in the journey is 1 minute.
Explanation:
Given data - The retardation from 30km/h to 15km/h takes a 1km distance. The acceleration from 15km/h to 30km/h takes 0.5km distance.
Case 1 - If there will be no retardation and acceleration and the train moves at a constant speed of 30km/h.
v = d/t
t = d/v
t = 1.5/30 = 1/20 hrs = 60/20 = 3 minutes.
Case 2 - If there will be retardation and acceleration according to the given data.
1) Retardation - v = 15km/h, u = 30km/h, s = 1 km
v² - u² = 2as
(15)² - (30)² = 2a(1)
a = - 675/2 km/h²
v - u = at
15 - 30 = (- 675/2)t
t = 2/45 hrs = 8/3 minutes
2) Acceleration - v = 30km/h, u = 15km/h, s = 0.5 km
v² - u² = 2as
(30)² - (15)² = 2a(0.5)
a = 675 km/h²
v - u = at
30 - 15 = 675t
t = 1/45 hrs = 4/3 minutes
Total time in the retardation and acceleration of the train is = 8/3 + 4/3 = 4 minutes.
Hence, the time lost in the journey = 4 - 3 = 1 minute.
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