Two cars A and B are moving with same speed 30km/hr in same direction with car B 5km behind the car A. Another car C moving in opposite direction crosses the two cars at an interval of 4 minutes. Find the speed of car C.
Let the car C be moving with velocity u km/hr.
Car B is 5 km behind the car A, therefore when the car C crosses car A, it is 5 km from car B.
Let us take left direction as positive and right direction as negative.
Velocity of car B = -5 km/hr
Velocity of car C = + u km/hr
The relative velocity of car C w.r.t car B is,
v = Velocity of car C - Velocity of car
= u - (-5) = (u + 5) km/hr
Now the car C travels 5 km distance with relative velocity (u + 5) km/hr in 4 minutes.
Therefore, using the relation s = ut, we have
, is the speed of car C.