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--- 183_notes:examples:holding_block_against_a_wall [2014/09/22 04:06] – pwirving
+++ 183_notes:examples:holding_block_against_a_wall [2014/09/22 04:16] (current) – pwirving
@@ Line 30: / Line 30: @@
 ==== Solution ====
-You need to identify whether the momentum in the y direction is negative (if it is, that would mean it was slipping down the wall).
+You need to identify whether the momentum in the y direction is negative (if it is, that would mean it was slipping down the wall, if it was positive it would mean it is slipping up the wall).
 Start by computing the change in momentum for both the x direction and the y direction.
-$ x: \Delta p_x = (F_{head} - F_N) \Delta t = 0 $
+$ x: \Delta p_x = (F_{hand} - F_N) \Delta t = 0 $
 $ y: \Delta p_y = (F_N - mg) \Delta t, \,\,assuming\, it\, slides $
-Combining these two equations, we have
+Combining these two equations
+$ (F_{hand} - F_N) \Delta t = 0 $
+$ F_{hand} \Delta t - F_N \Delta t = 0  \,\,\,\,\,\,\,Multiply\, out.$
+$ F_{hand} \Delta t = F_N \Delta t  \,\,\,\,\,\,\,\,\,Make\, equal\, to\, each\, other.$
+$ F_{hand} = F_N  \,\,\,\,\,\,\,\,\,\,\,\,Cancel\, \Delta t. $
+Substituting in we get:
 $ \Delta p_y = (F_{head} - mg) \Delta t = (0.6(40N) - (3 kg)(9.8 N/kg)) \Delta t $