# A system of two wheels fixed to each other is free to

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010 10.0points A system of two wheels fixed to each other is free to rotate about a frictionless axis through the common center of the wheels and per- pendicular to the page. Four forces are ex- erted tangentially to the rims of the wheels, as shown below. 2 F What is the magnitude of the net torque on the system about the axis? 10.0points In the absence of air resistance, a ball thrown vertically upward with a certain initial speed will return to its original level with the same speed. When air resistance is a factor affecting the ball, compare its speed to its initial speed when it returns to its original level. 1. less than its original speed correct 2. More information is needed. 3. the same as its original speed The three forces F apply counter-clockwise torques while the other force 2 F applies a clockwise torque, so τ = summationdisplay F i R i 011 10.0points Robin pushes a wheelbarrow by exerting a 147 N force horizontally. Robin moves it 83 m at a constant speed for 22 s. What power does Robin develop? 012 10.0points In the absence of air resistance, a ball thrown vertically upward with a certain initial speed will return to its original level with the same speed. When air resistance is a factor affecting the ball, compare its speed to its initial speed when it returns to its original level. 1. less than its original speed correct 2. More information is needed. 3. the same as its original speed
Version 050 – Midterm 02 – yao – (92695) 6 4. more than its original speed Explanation: The ball loses mechanical energy due to the negative work done by the air resistance, so when it returns to its starting point and to its original potential energy, it will have less kinetic energy and therefore less speed.
013 10.0points Two satellites A and B are orbiting the Earth in concentric circular orbits. Satellite B has twice the mass of satellite A, and the distance of satellite B from the Earth’s center is twice that of satellite A. What is the ratio of the tangential speed of B to that of A? v 0 m m What value of v 0 would be required in terms of g and ? 014 10.0points
Version 050 – Midterm 02 – yao – (92695) 7 E i = E f KE i + PE i = KE f + PE f 1 2 (2 m ) v 2 + 0 = 0 + (2 m ) g ℓ 1 2 parenleftbigg 1 2 v 0 parenrightbigg 2 = g ℓ v 0 = radicalbig 8 g ℓ = 2 radicalbig 2 g ℓ . 015 10.0points