A 8.8-kg mass is placed at (2.0, 3.0) m. Where can a 4.4-kg mass be placed so that the moment of inertia about the z axis is zero?Select one:a.(−1.0, −1.5) mb.(−4.0, −6) mc.(−2.0, −3.0) md.There is no position giving this result.e.(1.0, 1.5) m
Question
A 8.8-kg mass is placed at (2.0, 3.0) m. Where can a 4.4-kg mass be placed so that the moment of inertia about the z axis is zero?Select one:a.(−1.0, −1.5) mb.(−4.0, −6) mc.(−2.0, −3.0) md.There is no position giving this result.e.(1.0, 1.5) m
Solution
The moment of inertia (I) for a point mass is given by the equation I = m*r^2, where m is the mass and r is the distance from the axis of rotation. In this case, we want the total moment of inertia about the z-axis to be zero. This means that the moment of inertia of the 8.8-kg mass must be equal and opposite to the moment of inertia of the 4.4-kg mass.
The 8.8-kg mass is at (2.0, 3.0) m, so its distance from the z-axis is sqrt(2.0^2 + 3.0^2) = sqrt(13) m. Therefore, its moment of inertia is 8.8sqrt(13)^2 = 114.4 kgm^2.
The 4.4-kg mass must have a moment of inertia of -114.4 kg*m^2 to make the total moment of inertia zero. Since the moment of inertia is negative, the 4.4-kg mass must be placed on the opposite side of the z-axis from the 8.8-kg mass.
We can find the distance from the z-axis that the 4.4-kg mass must be placed at by rearranging the moment of inertia equation to solve for r: r = sqrt(I/m) = sqrt(-114.4/4.4) = sqrt(-26) m. Since the square root of a negative number is not a real number, there is no position that the 4.4-kg mass can be placed to make the total moment of inertia zero.
Therefore, the answer is d. There is no position giving this result.
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