Peoples Physics Concepts

4.5. Friction http://www.ck12.org

Question: F=?[N]

Given: m= 4. 7 kg

μk= 0. 68

g= 10. 0 m/s^2

Equations:∑F=ma

∑Fy=N−mg=^0 ,soN=mg

∑Fx=max

Fpull−fk= 0 (because the chair is moving atconstant s peed,soa= 0 )

Fpull=μkN

Plug n’ Chug:The force necessary to move the chair at a constant speed is equal to the frictional force between
the chair and the floor. However in order to calculate the frictional force you must first determine the normal force
which is (in this case) equal to the weight (i.e.Fg) of the chair.

N=mg= ( 4. 7 kg)( 10 m/s^2 ) = 47 N

Fpull=μkN= ( 0. 68 )( 47 N) = 32 N

Answer:

32 N

Example 2

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Watch this Explanation

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