JEE Advanced · 2012 · 08 Apr 2012 · Paper 2 · Kinematics

Two identical discs of same radius

R

are rotating about their axes in opposite directions with the same constant angular speed

ω

. The discs are in the same horizontal plane. At time

t = 0

, the points

P

and

Q

are facing each other as shown in the figure. The relative speed between the two points

P

and

Q

v_{r}

. In one time period

(T)

of rotation of the discs,

v_{r}

as a function of time is best represented by

(A)(see structure)
✓ Correct
(B)(see structure)
(C)(see structure)
(D)(see structure)

Answer: (A)

Solution

t = 0

, points

P

and

Q

are facing each other with velocities in opposite directions, giving maximum relative speed

v_{r} = 2 R ω

. As the discs rotate, the relative speed varies periodically. When the points are aligned along the line joining centers (twice per rotation),

v_{r}

is maximum. When perpendicular to this line (also twice per rotation),

v_{r}

is minimum (zero if they're at the same angular position relative to the line of centers). Option (A) shows this periodic variation with two maxima and two minima per period.

JEE Advanced · 2012 · 08 Apr 2012 · Paper 2 · Single correct option

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JEE Advanced · 2012 · 08 Apr 2012 · Paper 2 · Kinematics

Solution

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