A train crosses a platform in 43 seconds. The train’s length is 170 m, but the platform length is not given. What is the speed of the train?
-
A233 km/h
-
B243 km/h
-
C265 km/h
-
DCannot be determined
-
E60 km/h
Answer
Correct Answer: Cannot be determined
Explanation
Introduction / Context:When a train crosses a platform, the distance covered equals train length + platform length. Without the platform length, speed cannot be uniquely computed from time alone.
Given Data / Assumptions:
- Train length = 170 m.
- Time to cross platform = 43 s.
- Platform length = unknown.
Concept / Approach:Speed v = (L_train + L_platform) / t. Since L_platform is missing, v has infinitely many possible values depending on L_platform.
Step-by-Step Solution:
Let Lp be platform length. Then v = (170 + Lp)/43.Different Lp give different v; no unique v can be determined.Verification / Alternative check:If it were a signal post (Lp = 0), v = 170/43 ≈ 3.95 m/s (≈ 14.2 km/h), but platform is explicitly stated, so Lp ≠ 0.
Why Other Options Are Wrong:Numerical speeds like 233, 243, 265 km/h are unjustified without Lp. They are unrealistically high as well.
Common Pitfalls:Assuming platform length is zero; treating it as the same as a pole/post case.
Final Answer:Cannot be determined