Question

The speed of railway engine is 42 km per hour when no compartment is attached, and the reduction in speed is directly proportional to square root of the number of compartments attached. If the speed of the train carried by this engine is 24 km per hour when 9 compartments are attached, the maximum number of compartments that can be carried by the engine is:

• A. 49
• B. 48
• C. 46
• D. 47

Answer 1

The correct option is B 48

Speed S = 42 – K$\surd$(N) etc $\Rightarrow 24=42-K\surd 9\Rightarrow K=6.$
For engine to stop, $S=0\Rightarrow 0=42-6\surd n\Rightarrow n=49.$
With 49, it stops $\Rightarrow$ With 48, it will still move. Ans.(b)