IIT-JEE 2007 · Paper 1 · Physics Q16

← IIT-JEE 2007 · Paper 1

PhysicsSingle correct+4 / -1Question 16 of 66

Passage

Paragraph for Question Nos. 14 to 16

Two discs A and B are mounted coaxially on a vertical axle. The discs have moments of inertia $I$ and $2I$ respectively about the common axis. Disc A is imparted an initial angular velocity $2\omega$ using the entire potential energy of a spring compressed by a distance $x_1$ . Disc B is imparted an angular velocity $\omega$ by a spring having the same spring constant and compressed by a distance $x_2$ . Both the discs rotate in the clockwise direction.

(The paragraph is not printed in the official archive copy (which reproduces only the questions with their answers); its text is restored from the JEE 2007 question paper.)

The loss of kinetic energy during the above process is

\dfrac{I\omega^2}2

\dfrac{I\omega^2}3

\dfrac{I\omega^2}4

\dfrac{I\omega^2}6

Answer and worked solution

Official answer: B

Before: $\frac12I(2\omega)^2+\frac12(2I)\omega^2=3I\omega^2$ .

After: $\frac12(3I)\left(\frac43\omega\right)^2=\frac83I\omega^2$ .

Loss: $3I\omega^2-\frac83I\omega^2=\dfrac{I\omega^2}3$ .

(B)

Topics:Angular momentum and its conservation Rotational kinetic energy

← Previous question Next question →

IIT-JEE 2007 · Paper 1, Physics question 16