Two trains along the same straight rails moving the constant speed `60km//hr` and `30km//hr` respectively towards each other. If at time `t=0`, the distance between then is `90km`, the time when they collide is

The relative velocity of a body A with respect to a body B is the time rate at which body A changes its position with respect to body B . a)If V_A and V_B are the velocities of A and B moving in opposite directions,what is the relative velocity of A with respect to B ? b)Two trains along the same straight rails are moving with constant velocity of 60km/h and 30km/h towards each other.If at time t=0 ,the distance between them is 90km ,find the time when they collide. c)The velocity time graph of two bodies A and B make angles of 30° and 60° with the time axis,what is the ratio of their acceleration?

Two cars moving with speeds 40 km/hr and 80 km/hr respectively with uniform acceleration. How many times the stopping distance of car with 80 km/hr is greater than another car ?