Answer:
Part a)
[tex]a = 0.67 m/s^2[/tex]
Part b)
[tex]F_{max} = 107.1 N[/tex]
Explanation:
Part a)
Applied force on the block system is given as
[tex]F = 28 N[/tex]
total mass of the system is given as
[tex]m = M + 3M + 2M[/tex]
[tex]m = 6M[/tex]
now acceleration of the system is given as
[tex]a = \frac{F}{m}[/tex]
[tex]a = \frac{28}{6M}[/tex]
[tex]a = 0.67 m/s^2[/tex]
Part b)
When 3M mass block just start sliding then the force of friction on it will reach to its maximum value
[tex]F = F_s[/tex]
[tex]F = \mu_s (3M)(g)[/tex]
[tex]F = 0.26(3\times 7)(9.81)[/tex]
now the acceleration of the block is given as
[tex]a = \frac{F}{3M} = \mu_s g[/tex]
[tex]a = 0.26(9.81)[/tex]
[tex]a = 2.55 m/s^2[/tex]
now we have
[tex]F_{max} = (M + 2M + 3M) a[/tex]
[tex]F_{max} = 6(7)(2.55)[/tex]
[tex]F_{max} = 107.1 N[/tex]