Question

Two cars A and B were at town P. They wanted to travel to town Q. Car A started 15 minutes earlier than car B and maintained a constant speed of 20 m/s whereas car B started from rest and maintained a constant acceleration. Car A took 30 minutes to reach the destination. If car A and car B reached the destination simultaneously, then velocity with which car B reached is 

Answer 1

Given:

$t_A=30\:\rm min=1800\: s$

$t_B=15\:\rm min=900\: s$

$v_A=20\:\rm m/s=const$

$v_{Bi}=0$

The distance between Q and P

$$d=v_A*t_A=1800*20=36000\:\rm m$$

From the other side

$$d=\frac{v_{Bi}+v_{Bf}}{2}*t_B$$

Hence, the final velocity of car B

$$v_{Bf}=\frac{2d}{t_B}=\frac{2*36000}{900}=40\:\rm m/s$$