• # question_answer A running train crosses a stationary pole in 4 seconds and a platform 75 m long in 9 seconds. The speed of the train and its length is A)  42 m, 15 m/s B)  50 m, 15 m/s C)  60 m, 15 m/sec D)  45 m, 10 m/s

[c] Let the length of train be ?x? m Speed of train be ?y? m/sec. $\text{Given}\,\,\text{speed=}\frac{\text{distance}}{\text{time}}$ $y=\frac{x}{4}$                                   ? (1) and $y=\frac{x+75}{9}$                      ? (2) From (1) and (2) $\frac{x}{4}=\frac{x+75}{9}$ $\Rightarrow$ $9x=4x+300$ $\Rightarrow$ $x=60\,m$ $\therefore$ $y=\frac{60}{4}=15\,m/\sec$