Lab 3 - Dynamics

# Lab 3 - Dynamics - Physics 7A Dynamics Lab v.5.0 p 1 Name...

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Physics 7A Dynamics Lab, v.5.0 p. 1 Name ______________________________ Partner __________________________ Date _______________ GSI ___________________ Lab Day/Time _________ Lab 3: Dynamics Introduction This lab has two purposes. First, starting in the prelab, you’ll address increasingly difficult versions of a standard exam–level force problem about a cart and pulley. Then in lab you’ll test your answers experimentally. In addition, you’ll do experiments and answer questions designed to highlight some of the subtle conceptual aspects of Newton’s laws, and how these relate to common–sense force intuitions. Prelab Questions: An exam-level force problem [Complete these questions before coming to lab! Your GSI will discuss them at the beginning of the lab.] Consider the lab set-up below. A cart of mass m cart is connected to a vertically hanging mass, of mass m hang . The cart moves with negligible friction. In lab, you will give the cart a brief push away from the pulley , and then let it go. A. Draw separate free-body diagrams (FBDs) for the cart and for the hanging mass. Your diagrams should describe those objects after you finish pushing the cart , but while it’s still traveling away from the pulley . Label each force acting on each object. B. After you finish pushing the cart, what force (if any) is making the cart slide away from the pulley? Explain.

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Physics 7A Dynamics Lab, v.5.0 p. 2 C. In terms of m cart , m hang , and g , find the cart’s acceleration. Show your work here. (During the lab, you will plug in the relevant numbers, to make a numerical prediction.) D. Consider the time after the cart reverses direction and starts moving back towards the pulley. (i) In what ways, if any, must we modify the free-body diagrams from question A? Explain, and draw the correct FBDs here. (ii) Is the new acceleration bigger than, smaller than, or the same as the cart’s acceleration when it was traveling away from the pulley? Relate your answer to (i). End of pre-lab questions. The lab starts on the next page GSI’s Initials: ___________
Physics 7A Dynamics Lab, v.5.0 p. 3 1. In this first experiment, you’ll test your prelab prediction about the acceleration. Remove the brake from the cart, if it’s attached. Use a scale to measure m cart and m hang . Don’t forget to include the mass of the “hook” in m hang . With these values, predict the cart’s acceleration, using your answer to prelab question C. m cart = ________ m hang = ________ Predicted acceleration = _______________ If the track is currently set up as a ramp, lay it flat on the lab bench, and make sure it’s level. Using the computer software "

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Lab 3 - Dynamics - Physics 7A Dynamics Lab v.5.0 p 1 Name...

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