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Box on table has friction
 

coeff. of friction = uk 
Fnet = ma
make clockwise +
 
Mg - ukmg= (m + M)a
 
g(M-μkm) = a
(M+m)
 
Tension force in rope?
 

Rule  - One rope,
one tension

make clockwise +
Fnet = ma
 
T  - ukmg = ma
 
 
 
 
T  = ma + umg
 
Ex) T in terms of M
 
Draw freebody diagram for M
 
ΣFy=Ma
 
Mg -Tf  = Ma 
 
Tf = Mg - Ma
 
 
 

Massless, frictionless pulley and ramp
Find acceleration of red box up the ramp (M)

 
 
Masses move together with one accel.
make CCW +
 
Fnet = ma
 
 
mg - Mgsinq = (m + M)a

Hanging weight force
friction = ma

 

(m - Msinq)g = a
(M + m)

 

When does a = 0?

 

Msinq = m

When does box move down ramp?

(m - Msinq)g = a
(M + m)

When mg greater than MsinӨ>m

 


AP Friction

 

 

 

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