Q-7.A train 400m long is running at a speed of 72km/hr.How much time does it take to cross a telegraph post? please help fast!

Speed of the train = 72 km/hr = $\frac{72\times 1000}{60\times 60}=20\mathrm{m}/\mathrm{s}$

So, time taken to cross a telegraph post = $\frac{\mathrm{length}\mathrm{of}\mathrm{the}\mathrm{train}}{\mathrm{speed}\mathrm{of}\mathrm{the}\mathrm{train}}=\frac{400}{20}=20\mathrm{s}$

Therefore, it takes 20 second to cross a telegraph post.

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