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BITSAT2014PhysicsMotion in One DimensionActual

A train accelerating uniformly from rest attains a maximum speed of 40 ~ms ⁻¹ in 20 ~s . It travels at the speed for 20 ~s and is brought to rest with uniform retardation in further 40 ~s . What is the average velocity during the period ?

Options

  1. A80 ~m / s
  2. B25 ~m / s
  3. C40 ~m / s
  4. D30 ~m / s

Correct answer

B. 25 ~m / s

Step-by-step solution

(i) v = u + at ₁ array l 40=0+a 20 a=2 m / s² v²-u²=2 a s 40²-0=2 2 s₁ (ii) s₁=400 ~m (iii) v=u+a t 0=40+a 40 a=-1 ~m / s ² 0²-40²=2(-1) s ₃ ~s ₃=800 ~m Total distance travelled = s ₁+ s ₂+ s ₃ =400+800+800=2000 ~m Total time taken =20+20+40=80 ~s Average velocity = 2000 80 =25 ~m / s array

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