A metro train starts from rest and in 5 s achieves 108 km/h. 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.
12.2 s
15.3 s
9 s
17.2 s
D.
17.2 s
Given:- v= 108 km/h = 30 m/s
For first equation of motion
v = u + t
30 = 0 + × 5 ( u = 0)
⇒ a = 6 m/s2
So, distance travelled by metro train in 5s
=
Distance travelled before coming to rest = 45 m
So, from third equation of motion
⇒
⇒
Time taken in travelling 45 m is
= 3s
Now, total distance = 395 m
i.e 75 + s' + 45 = 395 m
i.e s' = 395 - (75 + 45)
⇒ s' = 275 m
∴ t2 =
t2 = 9.2 s
Hence, total time taken in whole journey
= t1 + t2 + t3
= 5 + 9.2 + 3
= 17.2 s
A tuning fork A produces 4 beats/s with another tuning fork B of frequency 320 Hz. On filing one of the prongs of A, 4 beats/s are again heard when sounded with the same fork B. Then, the frequency of the fork A before filing is
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316 Hz
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