If μsandμk represent the coefficients of static and kinetic friction with appropriate suffixes for the two bodies shown, find the acceleration of the system. Take g=10m/s2.
A
Zero
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B
4.2m/s2
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C
5.2m/s2
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D
10m/s2
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Solution
The correct option is C5.2m/s2 The given system can be shown in the FBDs as
So, we have from the above condition f1max=μs1(5g)=0.6×50=30N f2max=μs2(2g)=0.5×20=10N and, applied force =13g=130N
∵ the applied force > Total friction force of the system, the system will acclerate ∴ we have fk1=μk1(5g)=(0.4)(5g)=20N fk2=μk2(2g)=(0.3)(2g)=6N
So, from force equations: Taking the 5kg and 2kg masses as a system, we get 13g−T2=13a T2−fk1−fk2=(5+2)a13g−20−6=20a ⇒a=130−2620=5.2m/s2