Fisika Study Center

Physics.fisikastudycenter.com, Physics Olympiads problem series, olympiads preparation for beginner level, high school level. The needed basic concepts for this problems are forces (weight, frictional force, string tension), Newton's Laws.

Problem 13
Given three masses: m_A = 40 kg, m_B, dan m_C = 50 kg. The static frictional force coefficient between A and B is 0.3, between A the table is 0,2. See the figure!



Calculate the minimum mass of B so the system remains rest!
Question source: Fisika Study Center-Modification of UMPTN 1994 / Indonesian colleges examination entrance

Solution
Sketch the forces:



Analyze m_C that is in equilibrium conditions, both x axis and y axis, so then, ΣF = 0



m_B is in equilibrium conditions too, then ΣF_x = 0



Analyze m_A, apply equilibrium conditions to find the result:



Try This!
Given three masses that are m_A = 20 kg, m_B, dan m_C = 25 kg. The static frictional force coefficient between A and B is 0.3 and between A and the table is 0.2, see the figure!



Find the minimum mass of B, so that the system remains at rest!
Question source: Fisika Study Center-Modification of UMPTN 1994

answeri: 105 kg
prepared by : Fisika Study Center
Literatures/sources:
-UMPTN 1994 Questions
-tofi.or.id