A disc placed on a frictionless horizontal plank is rotating with a constant angualr velocity ( vec{omega} ) about its vertical axis. Now the plank is made to move with a constant acceleration ( vec{a} ) on a straight path. Initially the centre of the disc is at the origin of ( x y z ) space which is fixed with the plank and ( x y ) plane is on the plank. List-I gives some possible ( vec{a}, vec{omega} ) and List-II gives trajectories of instantaneous centre of rotation of the disc. begin{tabular}{|c|l|c|l|} hline multicolumn{2}{|c|}{ List ( -mathrm{I} )} & multicolumn{2}{|c|}{ List -II } hline (I) & ( overrightarrow{mathrm{a}}=-2 hat{mathrm{j}} mathrm{m} / mathrm{s}^{2}, vec{omega}=4 hat{mathrm{k}} mathrm{rad} / mathrm{s} ) & ( (P) ) & ( mathrm{y}=4 ) hline (II) & ( overrightarrow{mathrm{a}}=-2 hat{mathrm{j}} mathrm{m} / mathrm{s}^{2}, vec{omega}=-4 hat{mathrm{k}} mathrm{rad} / mathrm{s} ) & ( (mathrm{Q}) ) & ( mathrm{y}=4 mathrm{x}^{2}(mathrm{x} leq 0) ) hline (III) & ( overrightarrow{mathrm{a}}=-2 hat{mathrm{i}} mathrm{m} / mathrm{s}^{2}, vec{omega}=4 hat{mathrm{k}} mathrm{rad} / mathrm{s} ) & ( (mathrm{R}) ) & ( mathrm{y}=4 mathrm{x}^{2}(mathrm{x} geq 0) ) hline (IV) & ( overrightarrow{mathrm{a}}=-2 hat{mathrm{i}} mathrm{m} / mathrm{s}^{2}, vec{omega}=-4 hat{mathrm{k}} mathrm{rad} / mathrm{s} ) & ( (mathrm{S}) ) & ( mathrm{x}=4 mathrm{y}^{2}(mathrm{y} geq 0) ) hline & multicolumn{2}{|c|}{( (T) )} & ( mathrm{x}=4 mathrm{y}^{2}(mathrm{y} leq 0) ) hline end{tabular} Which one of the following options is correct? (A) I ( rightarrow mathrm{P} ), II ( rightarrow mathrm{Q} ), III ( rightarrow mathrm{T} ), IV ( rightarrow mathrm{S} ) (B) I ( rightarrow ) Q, II ( rightarrow ) R, III ( rightarrow ) S, IV ( rightarrow ) T (C) I ( rightarrow ) Q, II ( rightarrow ) S, III ( rightarrow ) T, IV ( rightarrow ) R (D) I ( rightarrow ) R, II ( rightarrow ) Q, III ( rightarrow ) S, IV ( rightarrow ) T
Question
A disc placed on a frictionless horizontal plank is rotating with a constant angualr velocity ( vec{omega} ) about its vertical axis. Now the plank is made to move with a constant acceleration ( vec{a} ) on a straight path. Initially the centre of the disc is at the origin of ( x y z ) space which is fixed with the plank and ( x y ) plane is on the plank. List-I gives some possible ( vec{a}, vec{omega} ) and List-II gives trajectories of instantaneous centre of rotation of the disc. begin{tabular}{|c|l|c|l|} hline multicolumn{2}{|c|}{ List ( -mathrm{I} )} & multicolumn{2}{|c|}{ List -II } hline (I) & ( overrightarrow{mathrm{a}}=-2 hat{mathrm{j}} mathrm{m} / mathrm{s}^{2}, vec{omega}=4 hat{mathrm{k}} mathrm{rad} / mathrm{s} ) & ( (P) ) & ( mathrm{y}=4 ) hline (II) & ( overrightarrow{mathrm{a}}=-2 hat{mathrm{j}} mathrm{m} / mathrm{s}^{2}, vec{omega}=-4 hat{mathrm{k}} mathrm{rad} / mathrm{s} ) & ( (mathrm{Q}) ) & ( mathrm{y}=4 mathrm{x}^{2}(mathrm{x} leq 0) ) hline (III) & ( overrightarrow{mathrm{a}}=-2 hat{mathrm{i}} mathrm{m} / mathrm{s}^{2}, vec{omega}=4 hat{mathrm{k}} mathrm{rad} / mathrm{s} ) & ( (mathrm{R}) ) & ( mathrm{y}=4 mathrm{x}^{2}(mathrm{x} geq 0) ) hline (IV) & ( overrightarrow{mathrm{a}}=-2 hat{mathrm{i}} mathrm{m} / mathrm{s}^{2}, vec{omega}=-4 hat{mathrm{k}} mathrm{rad} / mathrm{s} ) & ( (mathrm{S}) ) & ( mathrm{x}=4 mathrm{y}^{2}(mathrm{y} geq 0) ) hline & multicolumn{2}{|c|}{( (T) )} & ( mathrm{x}=4 mathrm{y}^{2}(mathrm{y} leq 0) ) hline end{tabular} Which one of the following options is correct? (A) I ( rightarrow mathrm{P} ), II ( rightarrow mathrm{Q} ), III ( rightarrow mathrm{T} ), IV ( rightarrow mathrm{S} ) (B) I ( rightarrow ) Q, II ( rightarrow ) R, III ( rightarrow ) S, IV ( rightarrow ) T (C) I ( rightarrow ) Q, II ( rightarrow ) S, III ( rightarrow ) T, IV ( rightarrow ) R (D) I ( rightarrow ) R, II ( rightarrow ) Q, III ( rightarrow ) S, IV ( rightarrow ) T
Solution
The question is asking to match the given acceleration and angular velocity vectors (List-I) with the corresponding trajectories of the instantaneous center of rotation of the disc (List-II).
The instantaneous center of rotation of the disc can be found by using the formula for the Coriolis effect, which is given by 2m(vec{v} x vec{ω}), where m is the mass of the disc, vec{v} is the velocity of the disc, and vec{ω} is the angular velocity of the disc.
Let's solve this step by step:
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For (I), vec{a} = -2j m/s² and vec{ω} = 4k rad/s. The acceleration is in the negative y-direction and the angular velocity is in the positive z-direction. This means the disc is moving downwards and rotating counterclockwise when viewed from above. The trajectory of the instantaneous center of rotation would be a straight line along the y-axis, so the correct match is (P) y = 4.
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For (II), vec{a} = -2j m/s² and vec{ω} = -4k rad/s. The acceleration is in the negative y-direction and the angular velocity is in the negative z-direction. This means the disc is moving downwards and rotating clockwise when viewed from above. The trajectory of the instantaneous center of rotation would be a parabola opening to the left, so the correct match is (Q) y = 4x² (x ≤ 0).
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For (III), vec{a} = -2i m/s² and vec{ω} = 4k rad/s. The acceleration is in the negative x-direction and the angular velocity is in the positive z-direction. This means the disc is moving to the left and rotating counterclockwise when viewed from above. The trajectory of the instantaneous center of rotation would be a parabola opening to the right, so the correct match is (R) y = 4x² (x ≥ 0).
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For (IV), vec{a} = -2i m/s² and vec{ω} = -4k rad/s. The acceleration is in the negative x-direction and the angular velocity is in the negative z-direction. This means the disc is moving to the left and rotating clockwise when viewed from above. The trajectory of the instantaneous center of rotation would be a parabola opening upwards, so the correct match is (S) x = 4y² (y ≥ 0).
So, the correct option is (A) I → P, II → Q, III → R, IV → S.
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