Two trains of length 100 meters and 200 meters are 840 meters apart. They are moving towards each other on parallel tracks, at speeds of 54 km/h and 72 km/h. After how many seconds will the trains meet?
Select.
A) 20 B) 22 C) 24 D) 26 E) 28
The speeds are 54000/3600= 
<gadget id="calculator">54000/3600</gadget>
<output>15</output>
15 m/s and 72000/3600= 
<gadget id="calculator">72000/3600</gadget>
<output>20</output>
20 m/s   The relative speed is 35 m/s.   time= 840 / 35= 
<gadget id="calculator">840 / 35</gadget>
<output>24</output>
24 seconds   The answer is 24.
<result>C</result>
Two trains of length 100 meters and 200 meters are 840 meters apart. They are moving towards each other on parallel tracks, at speeds of 54 km/h and 72 km/h. After how many seconds will the trains meet?