Question

a metro train starts from rest and in five seconds achieves 108 kmph . After that it moves with constant velocity and comes to rest after travelling 45 m with uniform retardation . If total distance travelled is 395 m , Find total time of travelling

Answer 1

Answer:

Explanation:

=>  A metro train starts from rest and in five seconds achieves 108 kmph.

u  = 0

v = 108 km/h = 30 m/s

t₁ = 5 s ec

v = u + at₁

a = 6 m/s²

Distnace covered in 5 seconds

s₁ = ut₁ + 1/2at₁²

s₁ = 1/2 * 6 * 5 * 5 = 75 m

=>  Here, After that it moves with constant velocity and comes to rest after travelling 45 m with uniform retardation and total distance travelled is 395 m.

Thus,  distance covered 395−75−45 = 275 m

v = 30 m/s

t₂ = distance/ velocity = 275/30 = 9.16 s ec

=> After travelling the distance of 45 m with uniform retardation a , metro comes to rest .

Thus, v = 0

v = u − at₃

0 = 30 −at₃

a = 30/t₃

Distance covered

s₃ = ut₃ −1/2at₃²

45 = 30t₃ − 15t₃

t₃ = 3 s ec

=> total time taken:

= t₁+t₂+t₃  

= 5 + 9.16 + 3

= 17.16 sec

Hence, total time of travelling is 17.16 seconds.