Question
Thu May 19, 2011 By: Prateek Kumar

what we have do is sum or subtraction when the two cars come from opposite direction and how?

Expert Reply
Thu May 19, 2011
When two cars come from opposite direction, you have to sum up their velocity when you are finding out their relative velocity.
 
For example
 
If the question is given that two cars 121 metre and 99 metres in length respectively are travelling in opposite directions, one at the rate of 40km per hour and the other at the rate of 32 km an hour.In what time will they be completely clear of each other from the moment they meet?
 
And the answer will be
As the two cars are moving in opposite directions their relative speed=40+32=72km/hr, i.e. they are approaching each other at 72 km/hr or 20m/sec.
therefore, the required time=
In this way you have to do the problem.
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