## Physics Olympiads Series Problem 13

- Category: Olympiads
- Written by fisikastudycenter

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