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Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Work and Energy

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Work and Energy

A simple pendulum consists of a 50 cm long string attached to a 100...

A simple pendulum consists of a 50 cm50 \text{ cm} long string attached to a 100 g100 \text{ g} ball. The ball is drawn aside until the string forms an angle of 37^{}^{{}^{\circ}} with the vertical, and is subsequently released. Determine the tension in the string when the bob reaches its lowest position.

Options

  1. A1.0 N1.0 \text{ N}
  2. B1.4 N1.4 \text{ N}
  3. C0.4 N0.4 \text{ N}
  4. D1.2 N1.2 \text{ N}

Correct answer

B. 1.4 N1.4 \text{ N}

Step-by-step solution

Given m=100 g=0.1 kgm = 100 \text{ g} = 0.1 \text{ kg}, L=50 cm=0.5 mL = 50 \text{ cm} = 0.5 \text{ m}, and \theta = 37^{}^{{}^{\circ}}.

The height descended by the bob from its initial position to the lowest point is:

h = L - L \cos \theta = L(1 - \cos 37^{}^{{}^{\circ}})

Substituting the values, we get:

h=0.5×(1−45)=0.5×0.2=0.1 mh = 0.5 \times \left(1 - \dfrac{4}{5}\right) = 0.5 \times 0.2 = 0.1 \text{ m}

Using the principle of conservation of mechanical energy, the velocity vv at the lowest point is given by:

12mv2=mgh⇒v2=2gh\dfrac{1}{2}mv^2 = mgh \Rightarrow v^2 = 2gh

Taking g=10 m/s2g = 10 \text{ m/s}^2, we have:

v2=2×10×0.1=2 m2/s2v^2 = 2 \times 10 \times 0.1 = 2 \text{ m}^2/\text{s}^2

At the lowest position, the net force towards the center provides the necessary centripetal acceleration:

T−mg=mv2LT - mg = \dfrac{mv^2}{L}

T=mg+mv2LT = mg + \dfrac{mv^2}{L}

Substituting the known values into the equation:

T=(0.1×10)+0.1×20.5T = (0.1 \times 10) + \dfrac{0.1 \times 2}{0.5}

T=1.0+0.4=1.4 NT = 1.0 + 0.4 = 1.4 \text{ N}
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