LOD II- Q38- 2 RIFLES FIRED 4RM SAME PLACEAT DIFF OF 11MIN 45SEC. BUT A MAN WHO IS COMMING TOWARDS THE PLACE IN A TRAIN HEARS THE SOUND AFTER 11MIN.FIND SPEED OF TRAIN??? a)72 km/h b)36 km/hr c)81 km/hr d)108 km/hr a)48 km/h b)36km/h c)54 km/h d)58 km/h
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A DOG AFTER TRAIVELLING 50 KM SLOWS AND PROCEEDS AT 3/4 OF HIS FORMER SPEED AND ARRIVES AT HIS DESTINATION 35 MIN LATE.HAD HE SLOWED AFTER MORE 24 KM THE DOG CUD HAV REACHED HIS DESTINATION 25 MIN LATE.THE SPEED OF DOG IS--
a)48 km/h b)36km/h c)54 km/h d)58 km/h
CASE I
If intial speed is v , after 50km the speed is 3v/4 i. e. reduced by v/4
Due to v/4 reduction in speed the time taken increase by 35/60 hr( = 7/12 hr)
We know Distance = Speed X Time
Let V1 = Velocity w/o speed reduced and T1 the time taken to cross the distance after 50km
and V2 = Velocity with the reduced speed and T2 the time taken to cross the distance after 50km
=> V1 T1 = V2 T2
=>V1 T1 = 3/4 V1 T2
=>T2 = 4/3 T1 = 1.33 T1
So differnce in time = .33T1 ; which is 7/12 hr
=> T1 = 21/12 hr
CASE II
HAD HE SLOWED AFTER MORE 24 KM THE DOG CUD HAV REACHED HIS DESTINATION 25 MIN LATE
Total distance V1 T1 = 21/12 V1
= 24 + 3/4 V1 [ 21/12 + 25/60 - 24/v1]
No solve the equation to get V1
anybody having any simpler method 2 solve this
the only diff. in timin comes for the xtra 24km that he travels in case 2
so..at speed x time taken=24/x
n at speed 3x/4 time taken =24/(3x/4)=16/x
the diff. is 10mins
so x is 48kph
Humraj
Q38- 2 RIFLES FIRED 4RM SAME PLACEAT DIFF OF 11MIN 45SEC. BUT A MAN WHO IS COMMING TOWARDS THE PLACE IN A TRAIN HEARS THE SOUND AFTER 11MIN.FIND SPEED OF TRAIN???
a)72 km/h b)36 km/hr c)81 km/hr d)108 km/hr
sol. we know speed of sound =330m/s = 1188km/hr
the distance cover by sound in 45 sec. = the distance cover by train in 11 min.
330x45 = 11x60xS
S = 22.5m/s = 81km/hr
Q50- A DOG AFTER TRAIVELLING 50 KM SLOWS AND PROCEEDS AT 3/4 OF HIS FORMER SPEED AND ARRIVES AT HIS DESTINATION 35 MIN LATE.HAD HE SLOWED AFTER MORE 24 KM THE DOG CUD HAV REACHED HIS DESTINATION 25 MIN LATE.THE SPEED OF DOG IS--
a)48 km/h b)36km/h c)54 km/h d)58 km/h
sol. let speed of dog is S km/hr.
24/(3/4)S - 24/S = 1/6hr
(24/S)x(1/3) = 1/6
S = 48km/hr
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