Two trains 12

Two trains 128m and 132m long are running towards each other on parallel lines at 42km/h and 30km/h respectively. In what time will they clear of each other from the moment they meet?

Correct answer:

t =  13 s

Step-by-step explanation:

$$\begin{gathered} a=128\text{m} \\ b=132\text{m} \\ {v}_1=42\text{km/h}\to \text{m/s}=42:3.6\text{m/s}=11.66667\text{m/s} \\ {v}_2=30\text{km/h}\to \text{m/s}=30:3.6\text{m/s}=8.33333\text{m/s} \\ s=a+b=128+132=260\text{m} \\ v=v_1+v_2=11.6667+8.3333=20\text{m/s} \\ t=\frac{s}{v}=\frac{260}{20}=13\text{s} \end{gathered}$$

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