A train moves past a telegraph post and a bridge 264 m long in 8 seconds and 20 seconds respectively. What is the speed of the train?

Given Data

• Passing a telegraph post in 8 s
• Passing a 264 m bridge in 20 s
• Required: speed of the train (km/hr)

Step 1: Let train length = L and speed = v m/s
Passing a post: L ÷ v = 8 ⇒ L = 8v

Step 2: Use the bridge crossing
Passing the bridge: (L + 264) ÷ v = 20Substitute L = 8v ⇒ (8v + 264) ÷ v = 208 + 264/v = 20 ⇒ 264/v = 12 ⇒ v = 22 m/s

Step 3: Convert to km/hr
Speed = 22 × (18/5) = 79.20 km/hr (rounded to 2 decimals)

Checks & Common Pitfalls

• Use train length only for passing a post to find v or L.
• For bridge/platform, add their length to the train's length.
• Convert m/s to km/hr by × 18/5 = 3.6.

Final Answer
The train's speed is 79.20 km/hr.