A beetle with a mass of 15.0 g is initially at rest on the outer edge of a horiz

Question

A beetle with a mass of 15.0 g is initially at rest on the outer edge of a horizontal turntable that is also initially at rest. The turntable, which is free to rotate with no friction about an axis through its center, has a mass of 95.0 g and can be treated as a uniform disk. The beetle then starts to walk around the edge of the turntable, traveling at an angular velocity of 0.0700 rad/s clockwise with respect to the turntable.

(a) With respect to you, motionless as you watch the beetle and turntable, what is the angular velocity of the beetle? Use a positive sign if the answer is clockwise, and a negative sign if the answer is counter-clockwise.
? rad/s

(b) What is the angular velocity of the turntable (with respect to you)? Use a positive sign if the answer is clockwise, and a negative sign if the answer is counter-clockwise.
? rad/s

(c) If a mark is placed on the turntable at the beetle's starting point, how long does it take the beetle to reach the mark again?

Explanation / Answer

Solved a similar question.Just flip the values to get the answer. Hope it helps.

Question:A beetle with a mass of 30.0 g is initially at rest on the outer edge of a horizontal turntable that is also initially at rest. The turntable, which is free to rotate with no friction about an axis through its center, has a mass of 70.0 g and can be treated as a uniform disk. The beetle then starts to walk around the edge of the turntable, traveling at an angular velocity of 0.0700 rad/s clockwise with respect to the turntable.
A), With respect to you, motionless as you watch the beetle and turntable, what is the angular velocity of the beetle? Use a positive sign if the answer is clockwise, and a negative sign if the answer is counter-clockwise.

SOLUTION:

From conservation of angular momentum.

Beetle's angular momentum with respect to the center of the turntable: Lb = Mb*vb*R
vb = b*R so Lb = Mb*b*R²
turntable angular momentum = Lt = I*t. I = moment of inertia = Mt*R²/2, Lt = (Mt*R²/2)*t

The sum of these must be zero, since the initial angular momentum of the system was zero:

Mb*b*R² + (Mt*R²/2)*t = 0

Mb*b + (Mt/2)*t = 0
Also
b - t = 0.700; b = t + 0.700

30.0*b + 35.0*t = 0
30.0*(t + 0.700) + 35.0*t = 0
65.0*t + 21.00 = 0

t = -0.323rad/s
b = -0.323 + 0.700 = +0.377 rad/s

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