phy 121
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Asst 25 Question 1
A steel ball of mass 110 grams moves with a speed of 30 cm / second around a circle of radius 20 cm.
What are the magnitude and direction of the centripetal acceleration of the ball?
answer/question/discussion: ->->->->->->->->->->->-> :
v^2/r = a
(30 cm/s)^2/20cm= 45 cm/s^2
f=ma
f=.110kg(.45m/s^2)= .05N
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What is the magnitude and direction of the centripetal force required to keep it moving around this circle?
answer/question/discussion: ->->->->->->->->->->->-> :
I assume that the .05N of force must be maintained to keep it moving.
It doesn't take any force to keep something moving; zero net force implies constant velocity, meaning constant speed and direction.
However this object keeps changing its direction as it goes around the circle, and this does take a net force, equal to the one you've calculated.
This force won't change the object's speed, only its direction. There might be other forces (air resistance to slow it, an engine to speed it up) that do change the object's speed, but the centripetal force remains directed toward the center, perpendicular to the object's velocity, and therefore does no work on the object.
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Revised: 06 Feb 2010 17:16:32 -0500
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15 min.
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4/6 at 9:03 p.m.
&#Good responses. See my notes and let me know if you have questions. &#
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