-
A train 800 metres long is running at the speed of 78 km/hr. If it crosses a tunnel in 1 minute, then the length of the tunnel (in metres) is :
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- 77200
- 500
- 1300
- 13
Correct Option: B
When a train crosses a tunnel, it covers a distance equal to the sum of its own length and
tunnel.
Let the length of tunnel be x
Speed = 78 kmph
| = | m/sec. = | m/sec. | ||
| 60 × 60 | 3 |
| ∴ Speed = | |
| Time |
| ⇒ | = | ||
| 3 | 60 |
⇒ (800 + x ) × 3 = 65× 60
⇒ 800 + x = 65 × 20 m
⇒ x = 1300 – 800 = 500
∴ Length of tunnel = 500 metres.
Second Method :
Here, x = 800 m,
u = 78 km/hr
| = 78 | = | m/sec | ||
| 18 | 3 |
t = 1 min = 60 sec, y = ?
using
| t = | |
| u |
| 60 = | |||||
| 3 | |||||
| 60 × | = 800 + y | |
| 3 |
1300 – 800 = y
y = 500 metres
