A block hangs at rest from the ceiling by a piece of rope. Consider the forces acting on the block. Is gravity present or absent
2 answers:
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Answer:
c. remains the same, but the RPMs decrease.
Explanation:
Because there aren't external torques on the system composed by the person and the turntable it follows that total angular momentum (I) is conserved, that means the total angular momentum is a constant:
The total angular momentum is the sum of the individual angular momenta, in our case we should sum the angular momentum of the turntable and the angular momentum of a point mass respect the center of the turntable (the person)
(1)
The angular momentum of the turntable is:
(2)
with I the moment of inertia and ω the angular velocity.
The angular momentum of the person respects the center of the turntable is:
(3)
with r the position of the person respects the center of the turntable, m the mass of the person and v the linear velocity
Using the fact :
(3)
By (3) and (2) on (1) and working only the magnitudes (it's all that we need for this problem):
Because the equality should be maintained, if we increase the distance between the person and the center of the turntable (r), the angular velocity should decrease to maintain the same constant value because I and m are constants, so the RPM's (unit of angular velocity) are going to decrease.
Answer:
5.0 m
Explanation:
The velocity of the object at time t is given by
where a=9.8 m/s^2 is the acceleration of gravity and t is the time. If we substitute v=7 m/s, we can find the time t at which the velocity became 7 m/s:
The height of the object at time t, h(t), is given by the equation
where is the initial height. By substituting t=0.71 s inside the equation, we find the height h(t) at which the velocity is 7 m/s: