Phys0174_1st-Midterm_solution

# Phys0174_1st-Midterm_solution - Phys0174 Midterm October 03...

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Phys0174 Midterm October 03 2008 Question 1: When you drive your car on a curve you always experience a force pushing you outward relatively to the car. This force is called the centrifugal force, which exists only in a rotating frame of reference, in this case the car. Consider the case in which the car is driving through a curve of radius R=10m at a speed of 20m/s. As a result, the centrifugal force pushes you against the car door. If your mass is 60kg, what is the magnitude of the centrifugal force acting on you? Explain using a force diagram. Since you are moving with the car, for an observer from the outside you will have a centripetal acceleration. The force that causes this acceleration is the normal force from the car on you F N . F N F cg Which means that R v m F N 2 = . However, relatively to the car you are not moving. This implies that the net force acting on you is zero. Therefore, there must be a force in that frame of reference that balances the normal force. That is the centrifugal force, and since it has to balance the normal force, that means if will have the same magnitude but act in the opposite direction. R v m F cg 2 =

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Question 2: Two friends are watching a bird flying above them and registering its location in time. The first finds that k j t i t r ˆ 20 ˆ 5 ˆ 2 2 1 + + = r . The second finds ( ) k j t i t t r ˆ 20 ˆ ˆ 2 6 2 2 + + = r . A) What is the location of the second friend relatively to the first?
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## This note was uploaded on 04/06/2009 for the course PHYS 0174 taught by Professor Kohler during the Spring '08 term at Pittsburgh.

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Phys0174_1st-Midterm_solution - Phys0174 Midterm October 03...

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