### torque

Question

ROTATION OF RIGID BODY

FIGURE 2.1(a) shows three children are playing on a merry-go-round which has a
moment of inertia of 271 kg m2
. Once the children get the merry-go-round spinning,
they stand evenly spaced around the outer edge as shown in FIGURE 2.1(b). Each
child has a mass of 28.0 kg, and the merry-go-round has a radius of 2.10 m.
(a) Assuming the moment of inertia of a child’s mass on the edge of the disc is
given by 𝐼 = 𝑚𝑟
2
, calculate the moment of inertia of the system.
[3 marks]
(b) While the merry-go-round is rotating at 2.31 m s-1
, one child drags her foot on
the ground to bring the merry-go-round to a stop in 2.80 s. Calculate the amount
of torque produced by the foot.
[3 marks]
(c) The children get the merry-go-round spinning once again at a constant angular
speed. Then each child moves inward towards the centre of the merry-go-round.
Using physics principles, explain the effect this has on rotational motion of the
merry-go-round.

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