IIT JEE , AIEEE Forum - Physics , Mechanics

zango_24

Two towns A and B are connected by a regular bus service with a bus leaving in either direction every T minute. A man cycling with a speed of 20km per hour in the direction of A to B notices that a bus goes past him every 18 minutes in the direction of his motion,and every 6 minutes in the opposite direction. The period of bus service is

A-18 minutes B- 6 minutes

C- 9 minutes C- 12 minutes

sboakarthik

answer is c 12 minutes

sboakarthik

D/v-20=18/60 -- i
D/v+20=6/60 --ii
solving for v & D
we get D=4km & v=20 km/hr
t=D/v
=1/5hrs
=12min (c)

pls inform me it its wrong

ramyani

Will you plz elaborate your answer.

sboakarthik

D is the distance between two towns
velocity of both the buses is assumed to be same
relative velocity of busses,
v-20 km/hr in the direction of cyclist
v+20 km/hr in the opp direction

applying in distance/velocity is time
we get the to equations
we get distance D & velocity

then we can find the time period of bus

ramyani

tnx. I rated u.

krishna.gopal

The concept used by karthik is right but there is a mistake in solving the equation. D/(v-20) will become infinite for v=20
he correct answer is v=40 km/hr and D=6 km
T = 6/40 hr = 9 mins

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