Question 1
Child runs and jumps on
playground merry-go-round.
For the system of the child +
disk (excluding the axle and
the Earth), which statement is
true from just before to just
after impact? ( K = total kinetic
energy, p = total linear
momentum, L = total angular
momentum about the axle)
1)
2)
3)
4)
5)
K , p , and L do not change
p and L do not change
L does not change
K and p do not change
K and L do not change
Question 2
What is the initial angular momentum
of the child + disk about the axle?
1) < 0, 0, 0 >
2) < 0, –Rmv, 0 >
3) < 0, Rmv, 0 >
4) < 0, 0, –Rmv >
5) < 0, 0, Rmv >
Question 3
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The disk has moment of inertia I,
and after the collision it is
rotating with angular speed .
The rotational angular
momentum of the disk alone
(not counting the child) is
1) < 0, 0, 0 >
2) < 0, –I, 0 >
3) < 0, I, 0 >
4) < 0, 0, –I >
5) < 0, 0, I >
Question 4
After the collision, what is the speed
(in m/s) of the child?
1) R
2) 
3) R2
4) R
5) 2R
(definition of radian measure, theta = arclength/radius so R=s,
divide by time to get v = R)
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Question 5
After the collision, what is the
translational angular momentum of
the child about the axle?
1) < 0, 0, 0 >
2) < 0, –Rm, 0 >
3) < 0, Rm, 0 >
4) < 0, –Rm(R), 0 >
5) < 0, Rm(R), 0 >
After the collision, what is the translational angular momentum of
the child about the axle? mvR = m(R)R= mR2 in - y direction
So Lf = Li
-mR2− I = − mvR
Question 6 (10.P.51)
What principle should
we use to find vs ?
Question 7 (10.P.51)
What principle should
we use to find f?
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1) The momentum principle
2) The energy principle
3) The angular momentum principle
1) The momentum principle
2) The energy principle
3) The angular momentum principle
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