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acerulz54
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Doc Al!--Blast from the Past
Hi Doc Al,
In 2004 you helped out a guy with this problem:
A 10 g coin of diameter 1.3 cm is spinning at 16 rev/s about a vertical diameter at a fixed point on a tabletop.
(a) What is the angular momentum of the coin about its center of mass?
(b) What is its angular momentum about a point on the table 10 cm from the coin?
(c) If the coin spins about a vertical diameter at 16 rev/s while its center of mass travels in a straight line across the tabletop at 5 cm/s, what is the angular momentum of the coin about a point on the line of motion?
(d) What is the angular momentum of the coin about a point 10 cm from the line of motion? (There are two answers to this question.)
You then responded:
This may help you: the angular momentum of an object is the sum of:
(1) the angular momentum of the center of mass
(2) the angular momentum about the center of mass
Thus:
a: See previous post
b: What's the movement of the center of mass?
c: See above
d: See above (there are two answers since you could be on either side of the line of motion)
2. I know I need 1/4 MR^squared for part a, but do I need 1/3 ML^squared for either b, c, or d?
3. I can handle part a, but but in part b I'm stuck: the center of mass is fixed there, but then in part c and d the cm travels in a straight line in the horizontal direction and I'm not sure how to take that into account. Can you help me? Thanks, and I'm glad a place like this exists for people like me!
Hi Doc Al,
In 2004 you helped out a guy with this problem:
A 10 g coin of diameter 1.3 cm is spinning at 16 rev/s about a vertical diameter at a fixed point on a tabletop.
(a) What is the angular momentum of the coin about its center of mass?
(b) What is its angular momentum about a point on the table 10 cm from the coin?
(c) If the coin spins about a vertical diameter at 16 rev/s while its center of mass travels in a straight line across the tabletop at 5 cm/s, what is the angular momentum of the coin about a point on the line of motion?
(d) What is the angular momentum of the coin about a point 10 cm from the line of motion? (There are two answers to this question.)
You then responded:
This may help you: the angular momentum of an object is the sum of:
(1) the angular momentum of the center of mass
(2) the angular momentum about the center of mass
Thus:
a: See previous post
b: What's the movement of the center of mass?
c: See above
d: See above (there are two answers since you could be on either side of the line of motion)
2. I know I need 1/4 MR^squared for part a, but do I need 1/3 ML^squared for either b, c, or d?
3. I can handle part a, but but in part b I'm stuck: the center of mass is fixed there, but then in part c and d the cm travels in a straight line in the horizontal direction and I'm not sure how to take that into account. Can you help me? Thanks, and I'm glad a place like this exists for people like me!