170. Four persons P, Q, R and S of same mass travel with same speed u along a square of side 'd' such that each one always faces the other. After what time will they meet each other?
(1) d/2
(2) 2d/3u
(3) 2d/u
(4) d√3
Answers
Answer:
Situation shown in figure. actually, every time the persons are approaching each other and hence they are moving closer and closer as they continue walking. finally they will meet at the centre of square.
from diagram, we find resultant displacement by each other when they meet will be d/√2
and the component of velocity of each towards the final point will be v/√2 .
so, time taken = displacement/velocity
= (d/√2)/(v/√2)
= d/v
so option a is right v=d/u
Answer:
(1) d/u
Explanation:
See I am taking velocity along the line joining PQ and right side positive.
So V(Q,P,D)=V(Q,D)-V(P,D)
V(Q,D)=ucos90=0
V(P,D)=u
therefore V(Q,P,D)=0-u= -u
initial separation between P and Q = d
final separation between P and Q = 0
Displacement = 0-d
= -d
time== Displacement/velocity==-d/-u=d/u...