Phys298Exam1Sp08-Solutions

# Phys298Exam1Sp08-Solutions - Phys 298 Brown Friday February...

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Phys 298 Brown Exam 1 Name ______________________________ Friday, February 8, 2008 This is a closed-book, closed-note, closed-neighbor exam. You are allowed one 3”x5” card with information, a calculator (not a computer), and your writing instruments. Multiple choice questions each have only one correct choice. Partial credit will be given on the ‘work-out’ problems. You may use the value g = 10 m/s 2 where needed. Good luck, and “May the Net Force be with you!” 1. An eccentric Physics professor sits in an airplane holding an unwound yo-yo such that it hangs straight down. As the plane accelerates down the runway toward take-off, the professor notices that the yo-yo string makes an angle θ with the vertical. What is the acceleration of the airplane? (Yes, I really did this once, traveling with a student to a research conference). a. g cos " b. g sin " c. g tan " d. g e. 0 F x = T sin " = ma F y = T cos " # mg = 0 \$ T cos " = mg % % T sin " T cos " = ma mg \$ a = g tan " 2. An object is moving a. There is a net force on the object in the direction of motion. b. There is a net force on the object in the direction opposite motion. c. No forces act on the object. d. Not enough information is given to comment on forces on the object. 3. An object is initially moving in the positive x-direction with speed v 0 . It is acted on for a time t by a net force in the negative y-direction. At the end of this time, what is the x-component of velocity? First, a moving object doesn’t HAVE to have a force acting on it – that’s an old Aristotelian idea. Second, we don’t know HOW the object is moving. A force in the y-direction doesn’t affect motion in the x-direction.

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