A train crosses a man standing on a 140 m long platform in 5 seconds and crosses the platform completely in 15 seconds. Find the length and speed of the train.

Let the length of the train be L m and the length of the platform be l m.

Let the speed of the train be V km/h.

The train crosses the platform in 15 seconds. 

So, t = (L + l)/V 

15 = (L + 140)/V -------------------------(1),

Now,the train crosses the man in 5 seconds. 

So, t = L/V

5 = L/V

L = 5V ---------------------------------(2),

From (1) and (2),

V = 14 m/s = 14 * 18/5 = 50.4 km/h

Now, putting the value of "V" in equation (2), we get

L = 5V 

L = 5*14 

L = 70 m 

So, the length and speed of the train are 70 m and 50.4 km/h, respectively.