Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
Concepts Of Physics MCQ Edition [Volume 1]
Exam
Concepts Of Physics MCQ Edition [Volume 1]
Subject
Physics
Chapter
Rotational Mechanics

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Rotational Mechanics

A uniform metre stick of mass 200 g is suspended from the ceiling...

A uniform metre stick of mass 200 g200 \text{ g} is suspended from the ceiling by two vertical strings of equal lengths attached at its ends. A small object of mass 20 g20 \text{ g} is positioned on the stick at a distance of 70 cm70 \text{ cm} from the left end. Determine the tensions in the two strings.

Options

  1. A1.14 N1.14 \text{ N} in the left string and 1.06 N1.06 \text{ N} in the right string
  2. B1.06 N1.06 \text{ N} in the left string and 1.14 N1.14 \text{ N} in the right string
  3. C1.12 N1.12 \text{ N} in the left string and 1.04 N1.04 \text{ N} in the right string
  4. D1.04 N1.04 \text{ N} in the left string and 1.12 N1.12 \text{ N} in the right string

Correct answer

D. 1.04 N1.04 \text{ N} in the left string and 1.12 N1.12 \text{ N} in the right string

Step-by-step solution

Let the length of the metre stick be L=100 cmL = 100 \text{ cm}.

Mass of the stick, M=200 g=0.2 kgM = 200 \text{ g} = 0.2 \text{ kg}.
Weight of the stick, W1=Mg=0.2×9.8=1.96 NW_1 = Mg = 0.2 \times 9.8 = 1.96 \text{ N}, acting at its centre of gravity (50 cm50 \text{ cm} from the left end).

Mass of the small object, m=20 g=0.02 kgm = 20 \text{ g} = 0.02 \text{ kg}.
Weight of the object, W2=mg=0.02×9.8=0.196 NW_2 = mg = 0.02 \times 9.8 = 0.196 \text{ N}, acting at 70 cm70 \text{ cm} from the left end.

Let T1T_1 and T2T_2 be the tensions in the left and right strings respectively.

For rotational equilibrium, taking torque about the left end:
T2×100=W1×50+W2×70T_2 \times 100 = W_1 \times 50 + W_2 \times 70
T2×100=(1.96×50)+(0.196×70)T_2 \times 100 = (1.96 \times 50) + (0.196 \times 70)
T2×100=98+13.72=111.72T_2 \times 100 = 98 + 13.72 = 111.72
T2=1.1172 N≈1.12 NT_2 = 1.1172 \text{ N} \approx 1.12 \text{ N}

For translational equilibrium, balancing the vertical forces:
T1+T2=W1+W2T_1 + T_2 = W_1 + W_2
T1+1.1172=1.96+0.196=2.156T_1 + 1.1172 = 1.96 + 0.196 = 2.156
T1=2.156−1.1172=1.0388 N≈1.04 NT_1 = 2.156 - 1.1172 = 1.0388 \text{ N} \approx 1.04 \text{ N}

Therefore, the tension in the left string is 1.04 N1.04 \text{ N} and in the right string is 1.12 N1.12 \text{ N}.

Answer: 1.04 N1.04 \text{ N} in the left string and 1.12 N1.12 \text{ N} in the right string
Practice Rotational Mechanics on Quantrex Academy →

More from Rotational Mechanics

A wheel revolves about its axis with a uniform angular acceleration. Beginning from rest… Concepts Of Physics MCQ Edition [Volume 1]Starting from rest, a wheel is uniformly accelerated at 4 rad/s^2 for 10 seconds.… Concepts Of Physics MCQ Edition [Volume 1]Determine the angular velocity of a body rotating with an acceleration of 2 rev/s^2 as it… Concepts Of Physics MCQ Edition [Volume 1]A body rotates about a fixed axis with an angular acceleration of one… Concepts Of Physics MCQ Edition [Volume 1]A disc of radius 10 cm rotates about its axis with an angular speed of 20 rad/s .… Concepts Of Physics MCQ Edition [Volume 1]A disc of radius 10 cm rotates about its axis with an angular speed of 20 rad/s .… Concepts Of Physics MCQ Edition [Volume 1]A disc rotates about its axis with a uniform angular acceleration of 4 rad/s^2 .… Concepts Of Physics MCQ Edition [Volume 1]A block is suspended from a string wrapped on a disc of radius 20 cm , which is free to… Concepts Of Physics MCQ Edition [Volume 1] Full Rotational Mechanics list All Concepts Of Physics MCQ Edition [Volume 1] PYQs