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Phy 101 2008 Exam 3

# Phy 101 2008 Exam 3 - 1 A merry-go-round spins freely when...

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1. A merry-go-round spins freely when Janice moves quickly to the center along a radius of the merry-go-round. It is true to say that (A) the moment of inertia of the system decreases and the angular speed increases. (B) the moment of inertia of the system decreases and the angular speed decreases. (C) the moment of inertia of the system decreases and the angular speed remains the same. (D) the moment of inertia of the system increases and the angular speed increases. (E) the moment of inertia of the system increases and the angular speed decreases. 2. A store's sign, with a mass of 20.0 kg and 3.00 m long, has its center of gravity at the center of the sign. It is supported by a loose bolt attached to the wall at one end and by a wire at the other end, as shown in the figure below. The wire makes an angle of 25.0° with the horizontal. What is the tension in the wire? (A) 108 N (B) 98 N (C) 232 N (D) None of these ( ) ( ) τ = τ = = cw ccw 2 Locate the pivot point at the bolt. (1.50m) 20.0kg 9.8m / s (3.00m)(Tsin25 ) T 232N 3. The L-shaped object shown in the figure below consists of the masses connected by light rods. How much work must be done to accelerate the object from rest to an angular speed of 3.25 rad/s about the x -axis?

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( ) ( ) ( ) ( ) 2 2 2 1 2 Total f x x 2 2 1 2 Total W K K 0 I I 2 (1kg)(1.8m) 6.48kg m W 6.48kg m 3.25rad / s 34.2J = Δ = - = ω = = = = 4. The acceleration due to gravity on the surface of Earth is g . Calling R the radius of Earth, at what distance from Earth's center would the acceleration due to gravity drop to g/16? (A) 16 R (B) R/4 (C) 4 R (D) R/16 ( ) ( ) ( ) = = = = ! ! E E E 2 2 2 E E E g GM GM GM g 16 R R 16 R R 4R
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