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# The Acceleration of the Train Starting from Rest at Any Instant is Given by the Expression a = 8 V 2 + 1 Where V is the Velocity of Train in M/S. - Engineering Mechanics

Answer in Brief

The acceleration of the train starting from rest at any instant is given by the expression a=8/(v^2+1) where v is the velocity of train in m/s. Find the velocity of the train when its displacement is 20 m and its displacement when velocity is 64.8 kmph.

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#### Solution

Given : a=8/(v^2+1)
To find : Velocity when displacement is 20 m
Displacement when velocity is 64.8 kmph.
Solution :
a=v(dv)/(dx)
v(dv)/(dx)=8/(v^2+1)
v(v2+1)dv = 8dx
Integrating both sides
∫ v(v2+1)dv = ∫ 8dx
(v^2)/(4)+(v^2)/(2)=8x+c……….(1)
Multiplying by 4 on both sides
V4 + 2v2 = 32x + 4c
Substituting v=0 and x=0 in (1)
c=0 From (1)
V4 + 2v2 = 32x ………….(2)
Case 1 : x=20 m
V4 + 2v2 = 32 x 20 ………(From 2)
V4 + 2v2 – 640 = 0
Solving the equation
V2 = 24.3180
V=4.9361 m/s
184 + 2 x 182 = 32x …………..(From 2)
1.5624 = 32x
x = 3300.75 m
When displacement of train is 20 m,then velocity is 4.9361 m/s
When velocity of the train is 64.8 kmph,then its displacement is 3300.75m

Concept: Beams Support
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