CT12-1. A small wheel and a large wheel are connected by a belt. The small wheel is turned at a constant angular velocity s. How does the magnitude of the angular velocity of the large wheel L compare to that of the small wheel?Pink: s = LGreen: s > LYellow: s < LAnswer: s > L Every time the big wheel turns once, the little wheel turns several times. So the small wheel turns thru more radians per sec.There is a bug S on the rim of the small wheel and another bug L on the rim of the large wheel. How do their speeds compare?Pink: S = L Green: S > L Yellow: S < LAnswer: S=L. Because the wheels are connected by a belt which does not slip, when one bug moves an inch along the rim, so does the other bug.sLCT12-2. A ladybug is clinging to the rim of a spinning wheel which is spinning CCW very fast and is slowing down. At the moment shown, what is the approximate direction of the ladybug's acceleration?Answer: You can see this in two ways. avt or a a atot r t The tangential component of the acceleration points "backwards" because the wheel is slowing down.CT12-3 A student in Physics 1110 sees the following question 1 on CAPA set 10(Due Friday Oct.30).An engine flywheel turns with constant angular speed of 100 rev/min. When the engine isshut off, friction slows the wheel to rest in 2 hours. What is the magnitude of the constant angular acceleration of the wheel? (Answer in rev/min2).The student writes oorevttft, ,( )min.min02 2 100120 so Pink: Yellow:Blue:Green: Purple: None of these.v1 v v2 ar atot atDoes the answer come out correctly with the desired units?Green: Yes Pink: NoAnswer: No! You would write the exactly the same equations above if you were trying toget the answer in rad/min2. The factor of 2 in the equation is actually 2 rad/rev, so theunits of the answer above are really rad/min2. If you want the answer in rev/min2, you have to leave out the factor of 2 , or you can convert the answer in rad/min2 to rev/min2 by multiplying by the conversion factor (1 rev/2 rad).CT12-4 Three forces labeled A, B, C are applied to a rod which pivots on an axis.Which force causes the largest magnitude torque? Pink: A Yellow: B Green: CBlue: two or more forces tie for largest size torque.Answer: A. For C, LF LF4212. For B, LF LF212. For A, LF LFosin( ) .45 0 707.2F F F 45o L/4 L/2 L A C BCT12-5. A mass is hanging from the end of a horizontal bar which pivots about an axis through it center, but it being held stationary. The bar is released and begins to rotate. Asthe bar rotates from horizontal to vertical, the magnitude of the torque on the bar..Pink: increases Green: decreases Blue: remains constantAnswer: The torque decreases! F r F r sin F decreases as the mass falls. When the bar is vertical the torque is zero.As the bar rotates from horizontal to vertical, the magnitude of the angular acceleration of the bar..Pink: increases Green: decreases Blue: remains constantAnswer: decreases. I . Here I, the moment of inertia, is constant. The torque decreases (problem above), so the angular acceleration must decrease. rFFCT12-6. A mass m hangs from string wrapped around a pulley of radius R. The pulley has a moment of inertia I and its pivot is frictionless. Because of gravity the mass falls and the pulley rotates.The magnitude of the torque on the pulley is..Pink: greater than mgRGreen: less than mgRYellow: equal to mgR(Hint: Is the tension in the string = mg?)Answer: The magnitude of the torque is less than mgR! The tension in the string is less than mg because the mass is accelerating down. Considering the motion of the mass m, we get…F mg F ma F mg manet T T Considering the motion of the pulley, we get…Torque F R I IaRT Two equations [FT = mg-ma, FT = I a/(R2)] in two unknowns (FT and a) can
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