# Lab 4

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The Mass-Dependence of Friction 1. Make free-body diagrams of a cart moving up and down the track. Label the forces. 2. Based on the above, write out Newton’s Second Law for each direction for both situations. Remember to show your work, eg., the arguments for your derivation of the variable f. 3. Solve the above equations for N, f, and μ. Answers must be in terms of m, g, a u , a d , and θ. Remember to show your work. 4. Insert into the box the v x (t) graphs for the three measurements, with data and boxes readable. WPI Physics Department 1 PH 1110 2014-15 Name and section number: Emily Stratton Partner’s name and section number: Josh Boynton Up: Σ F x = ma u = Down: Σ F x = ma d = Σ F y = 0 = Σ F y = 0 = N = m g cos ( θ ) f = m 2 ∗( a u a d ) μ = ( a u a d ) 2 g cos ( θ )

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WPI Physics Department 2 PH 1110 2014-15 a) b) c)
5. Fill in this table, stating the units within the square brackets, and using four significant figures. If you are pressed for time, collect data now (yellow boxes) and calculate later (green). Trial θ [°] m [kg] a u [m/s 2 ] a d [m/s 2 ] N [] f [] μ [] 1 3.92 0.498
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