Expert: Richard J. Raridon - 9/2/2004

Question
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Followup To
Question -
1. A was travelling in a Lancer with a speed 72 km/hr. B was travelling in another car in the same direction with a speed of 90 km/hr. A truck 400 mt. away and travelling in the opposite direction took 10 seconds to cross B. How much time did the truck take to cross A after it crossed B, if the distance between A's car & B's car initially was 300mt?
Answer -
what unit is mt?
what do you mean, 10 seconds to cross B?   Is that 10 seconds before meeting B?

mt is meter. 10 seconds to cross B means that the truck takes 10 secs. to cross B.

Answer
First of all, the abbreviation for meter is m.  
72km/hr = 20m/s
90km/hr = 25m/s
I assume that the truck was 400m from B.  
Since B will travel 250m in 10s, the truck travels 150m
so it has a speed of 15m/s.  
A will travel 200m in 10s so it and the truck will be
350m apart.  Since the combined speed of A and the truck is
35m/s, they will cross in another 10s.