Find the acceleration of the blocks A and B in the three situations shown in figure
(5-E 17).



Given: 5a + T − 5g = 0


From free-body diagram (1), T = 5g − 5a …..(i)



T 8g 16a = 0


From free-body diagram (2),


T = 8g + 16a ……(ii)


From equations (i) and (ii), we get:


5g − 5a = 8g + 16a



So, the acceleration of the 5 kg mass is 97 m/s2 upward and that of the 4 kg mass is 2a= downward.


(b) From free body diagram (3),


8a T = 0


T = 8a


Again, T + 5a − 5g = 0


From free body diagram-4, 8a + 5a − 5g = 0


13a 5g = 0


downward


(c) T + 1a − 1g = 0


From free body diagram, T = 1g − 1a …..(i)


Again, from free body diagram


T 4g 8a = 0 ..(ii)


From equation (i) 1g − 1a − 4g − 8a = 0


downward


Acceleration of mass 1 kg is upward, Acceleration of mass 2 kg is downward


2