Question

Two blocks of mass m1 = 7 kg and m2 = 6 kg connected with a light in-extensible string are placed on a horizontal table. A third block of mass m=3 kg is attached with a string to block 2 over a pulley and hangs off the edge of the table. The coefficient of friction between the first block and the table is µ1 = 0.2, between the second block and the table is µ2 = 0.1. Find the tension in both strings and the friction forces between the table and both blocks

Answer 1

g =9.81 m/s^2

F1= friction force on m1 = 0.2 * 7 g = 1.4 g
F2 = friction force on m2 = 0.1 * 6 g = 0.6 g

F3 = gravity force down on m3 = 3 g

T2 = tension on blocks 2 and 3
for block3:
3 g - T2 = 3 a

T1 = tension on blocks 1 and 2
block2:
T2 - T1 - 0.6 g = 6 a

block 1
T2 - 1.4 g = 7 a

so three equations and three unknowns T1, T2, a ,(remember g = 9.81)
T2 - 1.4 g = 7 a
T2 - T1 - 0.6 g = 6 a
3 g - T2 = 3 a

Answer 2

thankss! can I just solve for the unknowns simultaneously?

Answer 3

Precisely