Question

A train whose proper length is 1200 m passes at a high speed through a station whose platform measures 900 m, and the station master observes that when the train passes it occupies exactly the entire length of the platform. What is the speed of the train?

Answer 1

0.66c

Step-by-step explanation:

Use length contraction equation:

L = L₀ √(1 − (v²/c²))

where L is the contracted length,

L₀ is the length at 0 velocity,

v is the velocity,

and c is the speed of light.

900 = 1200 √(1 − (v²/c²))

3/4 = √(1 − (v²/c²))

9/16 = 1 − (v²/c²)

v²/c² = 7/16

v = ¼√7 c

v ≈ 0.66 c