Problem 3: The static coefﬁcient of friction usis larger than the kinetic coefﬁcient pk. In the previous problem

you measured us. Here we attempt to measure pk. The procedure is as follows: 1) set up the inclined plane at an

angle that is 10 degrees more than that which was determined as the angle in which the static block broke free.

2) Practice releasing and measuring the time t that the same block travels down the incline Ax. Once you have

consistent results, repeat the experiment four times and record the data below. Table 3: Experimental Data for pk n-—— tTrial3 Averagettseconds) To calculate uk we follow a similar approach as used in the previous problem: Applying Newton's Law in the x

and y directions, produces: x : —f+ Wsina = ma and y : N — Wcosﬁ = 0. Since W: mg, analysis in the y—direction

gives us: N = mgcose. The deﬁnition of the frictional force is f = ukN, then f = ukmgcose, which in turn can be

inserted into -f+ Wsine = ma producing —ukmgc059 + mgsin6 = ma. Therefore, _ gsinf) — a #k gum-6 (2) Calculating ﬂk via Equation 2 requires the acceleration a, the acceleration due to gravity 9, and the angle of the

2 ‘ _ _ 2A1-

incline 6. Use A”: 2 ”It + §at to ﬁnd a. For 1 I ‘ 0' a " 75‘. Again, Ax is the distance that the block traveled down the inclined plane corresponding to the time tyou measured and recorded in the previous table.

How does your measurement of ,uk and it; compare?