?Friction Equations - Multiple Parts Parts a, b, c, & d are about the same box,

Question

?Friction Equations - Multiple Parts

Parts a, b, c, & d are about the same box, under different conditions. The box's mass is m = 25kg. So, it's weight mg = 245 N. For a, b, & c, the box is sitting statically (not moving!) on a flat horizontal table. Figure a shows the box's free body diagram when the only forces acting are the normal force F_N upward & it's weight mg downward. Calculate F_N in this case. Figure b shows the free body diagram when, in addition to the normal force F_N & weight mg, an additional downward force F_p = 40 N acts on it when someone pushes on the top of it. Calculate F_N in this case. Figure c shows the free body diagram when, in addition to the normal force F_N & weight mg, an additional upward force F_P = 40 N acts on it when someone ties a rope around it & pulls up on it. Calculate F_N in this case. Figure d (at left!) shows the box's free body diagram when, similar to the case in Figure c, someone ties a rope around it & pulls up on it as shown. Now, however, the pulling force F_P = 280 N, which is large enough to cause the box to move upward. Calculate the box's acceleration in this case. In the case of part d, is there a normal force F_N acting on the box? Why or why not? What Physical Principle (or law) did you use to answer parts a, b, c, & d?

Explanation / Answer

(a) Fn-mg=0

Fn=mg=250N

(b) Fn=40+mg

(c)Fn+40=mg

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