Answer to Question #222111 in Physics for Faiza Tabrez

Question

Two cars A and B are at town P. They want to travel to town Q. Car A starts 15 minutes earlier than car B and maintains a constant speed of 20 m/s whereas car B starts from rest and maintains a constant acceleration. Car A takes 30 minutes to reach the destination. If car B wants to reach the destination at the same time the acceleration required 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

$$d=v_{Bi}t+a_Bt_B^2/2=a_Bt_B^2/2$$

Hence, the acceleration of car B

$$a_{Bf}=\frac{2d}{t_B^2}=\frac{2*36000}{900^2}=0.089\:\rm m/s^2$$