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su10EIIS

# su10EIIS - Physics 53 Summer 2010 Exam II Solutions Part A...

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Exam II Solutions Part A. Multiple choice questions. Check the best answer. Each question carries a value of 4 points. 1. Which of these general statements about a system of particles is wrong? Any change in total momentum comes from the action of external forces only. Any change in total kinetic energy comes from work done by external forces only. Any change in total angular momentum comes from the action of external torques only. Any change in total mechanical energy comes from work done by non-conservative forces only. 2. A symmetric body rolls without slipping. Which of these is wrong? If friction acts on the body, it is static friction. The body cannot roll up or down an incline without friction. Friction always acts opposite to the direction of the body’s CM motion. The body’s angular acceleration is proportional to its CM acceleration. Physics 53 Summer 2010 1

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3. A rigid body is rotating about an axis with angular velocity ω . If the axis passes through the CM then L is proportional to ω . If the axis is a symmetry axis of the body then L is proportional to ω . L is always proportional to ω . None of the above is true. 4. About spring tides and neap tides: Each happens once per lunar month. Spring tides result only when the sun and moon are on the same side of the earth. Spring tides happen at the time of full moon. Neap tides result when the sun and moon are on opposite sides of the earth. Physics 53 Summer 2010 2
Part B. True-false questions. Check T or F depending on whether the statement is true or false. Each question carries a value of 3 points. 5. The total momentum of a system is equal to the total mass times the velocity of the CM.

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