Car A and car B are both travelling down a straight highway at 90 km/h. car A is only 6.0 meters behind car B. the driver of car B brakes , slowing down with a constant deceleration of 2.0 `m//s^(2)`. After 1.2 seconds, the driver of car A begins to brake, also at `2.0 m//s^(2)`, but this is insufficient and the cars eventually collide, both still moving forward. what is the relative velocity of the two cars at the moment of the collision ?

Options

A. 2.4 m/s
B. 5.0 m/s
C. 9.5 m/s
D. 21 m/s

Answer

A

Explanation

`S_(rel)=u_(rel)t-1/2 are l t^(2)`
`=0-1/2 xx2xx1.2^(2) =-1.44 m`
`v_(rel)=u_(rel)-a_(rel)t=0-2xx1.2=-2.4 m//s`