Q89 / 180 · NEET 2020 (Phase 2) · Physics

A person sitting in the ground floor of a building notices through the window, of height 1.5 m, a ball dropped from the roof of the building crosses the window in 0.1 s. What is the velocity of the ball when it is at the topmost point of the window? g=10 m s-2

  • A
    15.5 m s-1
  • Correct answer
    B
    14.5 m s-1
  • C
    4.5 m s-1
  • D
    20 m s-1

Solution

First, recall the second equation of motion of kinematics, in terms of initial speed, time, and uniform acceleration, s=ut+12at2. Now make a diagram related to motion of the particle, 

Figure

then put the values in second equation of motion, 

⇒1.5=u(0.1)+12(10)(0.1)(0.1)⇒15=u+0.5

⇒u=14.5 m s-1.

Hence, the correct answer is option: 'B'.

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