Q65 / 90 · JEE Main 2024 (29 Jan Shift 2) · Physics

The bob of a pendulum was released from a horizontal position. The length of the pendulum is 10 m. If it dissipates 10% of its initial energy against air resistance, the speed with which the bob arrives at the lowest point is: [Use, g=10 m s-2 ]

  • Correct answer
    A
    65 m s-1
  • B
    56 m s-1
  • C
    55 m s-1
  • D
    25 m s-1

Solution

Figure

Given the length of the pendulum is ℓ=10 m.

The initial potential energy of the pendulum at the horizontal position is given by

U=mgℓ   ...1

The final kinetic energy of the pendulum at the lowermost position is given by

K=12mv2   ...2

So, from equations (1) and (2), it follows that

910mgℓ=12mv2⇒910×10×10=12v2⇒v2=180⇒v=180=65  m s-1

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

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