-
A man standing on a 170 metre long platform watches that a train takes
the platform. Find the speed of train.7 1 seconds to pass him and 21 seconds to cross 2
-
-
12 16 m/sec. 27 - 12.5 m/sec.
-
12 13 m/sec. 27 - None of these
-
Correct Option: A
Let the length of the train be x m and its speed y m/sec.
Distance covered in crossing the platform = 170 + x metres
and time taken = 21 seconds
| ∴ Speed y = | ...(i) | |
| 21 |
Distance covered to cross the man = x metres
| and time taken = 7 | = | seconds | ||
| 2 | 2 |
| ∴ Speed y = | = | ...(ii) | ||
| 15/2 | 15 |
From equations (i) and (ii),
| = | ||
| 21 | 15 |
⇒ 2550 + 15x = 42x
⇒ 42x – 15x = 2550
⇒ 27x = 2550
| ⇒ x = | = 94 | metres | ||
| 27 | 9 |
From equation (ii),
| y = | |
| 15 × 27 |
| = | = 12 | m per sec. | ||
| 27 | 27 |
| Hence, speed = 12 | m per sec. | |
| 27 |
