Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
NEET 2015
Exam
NEET
Year
2015
Subject
Physics
Chapter
Rotational Motion

NEET 2015 · Physics · Rotational Motion

A force → F = α ^ i + 3 ^ j + 6 ^ k is acting at a point → r = 2 ^...

A force \overset{\to}{F} = \alpha\overset{^}{i} + 3\overset{^}{j} + 6\overset{^}{k} is acting at a point \overset{\to}{r} = 2\overset{^}{i} - 6\overset{^}{j} - 12\overset{^}{k} . The value of α\alpha for which angular momentum about origin is conserved is:

Options

  1. A2\text{2}
  2. BZero
  3. C1\text{1}
  4. D−1- 1

Correct answer

D. −1- 1

Step-by-step solution

If L→=\overset{\to}{L} = constant then τ→=0\overset{\to}{τ} = 0

So r→×F→=0⇒F→\overset{\to}{r} \times \overset{\to}{F} = 0 ⇒ \overset{\to}{F} should be parallel to r→\overset{\to}{r} so coefficient should be in same ratio. So α2=3−6=6−12\dfrac{\alpha}{2} = \dfrac{3}{- 6} = \dfrac{6}{- 12}

So α=−1\alpha = - 1
Practice Rotational Motion on Quantrex Academy →

More from Rotational Motion

A solid sphere A of radius R and mass M is attached at a point to a smaller solid sphere… NEET 2026The angular speed of a flywheel is increased from 600 rpm to 1200 rpm in 10 s. The number… NEET 2026A thin wire of length ' L ' and linear mass density ' m ' is bent into a circular ring… NEET 2026A thin horizontal disc is rotating about a vertical axis passing through its fixed centre… NEET 2026The Sun rotates around its centre once in 27 days. What will be the period of revolution… NEET 2025A sphere of radius R is cut from a larger solid sphere of radius 2 R as shown in the… NEET 2025The radius of gyration of a solid sphere of mass 5 kg about X Y is 5 m as shown in… NEET 2024A wheel of a bullock cart is rolling on a level road as shown in the figure below. If its… NEET 2024 Full Rotational Motion list All NEET PYQs