Q13 of 57 Page 97


The free body diagram of the given system is shown above. Let us consider that the 15kg block is moving downward with the acceleration a.


From figure (a)


T + mamg = 0


T + 15a − 15g = 0


T = 15g − 15a……. (i)


From the figure (c)


T1 mgma = 0


T1 − 5g − 5a = 0


T1 = 5g + 5a ………. (ii)


From figure (b)


T = (T1 + 5a + μR) = 0


T − (5g + 5a + 5a +μR) = 0 ……. (iii)


(where R = μg)


From Equations (i) and (ii),
15g − 15a = 5g + 10a + 0.2 (5g)
25a = 90


a = 3.6 m/s2


From Equation (iii),
T = 5 × 10 + 10 × 3.6 + 0.2 × 5 × 10


T= 96 N in the left string.


From Equation (ii),
T1 = 5g + 5a
= 5 × 10 + 5 × 36
= 50 + 18
T1= 68 N in the right string
.


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