Two cars A and B are moving in the same direction along a straight line with speeds 100 km/h and 80 km/h, respectively such that car A is moving ahead of car B. A person in car B throws a stone with a speed v so that it hits the car A with a speed of 5 m/s. The value of v is km/h.
- 18
- 28
- 38
- 48
Answer
(3) 38
Solution
Take the direction of motion as positive. The stone is thrown forward with speed v relative to car B.
Velocity of the stone w.r.t. ground =(80+v) km/h
Required speed of the stone relative to car A: 5 m/s=5 185=18 km/h
(80+v)-100=18
v=38 km/h
Answer: (3)