Question : Train A is moving along two parallel rail tracks towards north with speed 72 km/h and train B is moving towards south with speed 108 km/h. Velocity of train B with respect to A and velocity of ground with
respect to B are (in m/s) :
(a) -30 and 50
(b) -50 and -30
(c) -50 and 30
(d) 50 and -30
JEE [1st Feb 2024, Shift 2]
Doubt by Faisal
Doubt by Faisal
Solution :
VA=+72 km/h (Towards North)
VA=+72×(5/18)
VA=+20 m/s
VA=+72×(5/18)
VA=+20 m/s
VB=-108 km/h (Towards South)
VB=-108(5/18)
VB=-30 m/s
VB=-108(5/18)
VB=-30 m/s
Velocity of Train B w.r.t. Train A
VBA=VB-VA
VBA=-30-(20)
VBA=-30-20
VBA=-30-(20)
VBA=-30-20
VBA=-50 m/s
-ve sign shows that the train B is moving towards south w.r.t to train A.
-ve sign shows that the train B is moving towards south w.r.t to train A.
Velocity of Ground (VG)=0 m/s
Velocity of Ground w.r.t. Train B
VGB=VG-VB
VGB=0-(-30)
VGB=0+30
VGB=+30 m/s
The +ve sign show that ground appears to move towards North w.r.t Train B.
VGB=VG-VB
VGB=0-(-30)
VGB=0+30
VGB=+30 m/s
The +ve sign show that ground appears to move towards North w.r.t Train B.
So, (c) -50 and 30, would be the correct option.