Friction problem of a 6kg block

[BallerRegis]

A 6 kg block rests on a horizontal table, attached to a 5 kg block by a light string as
shown in the figure.
The acceleration of gravity is 9.81 m/s2 .

A) What is the minimum coefficient of static
friction such that the objects remain at rest?

I already got part A which is 0.833, but need help on B


B) If the coefficient of static friction is less than
that found above, and if the coefficient of
kinetic friction between the block and the
table is 0.2, find the time it takes for the 5 kg
mass to fall 9 m to the floor if the system
starts from rest.
Answer in units of s

 

[PeterO]

A 6 kg block rests on a horizontal table, attached to a 5 kg block by a light string as
shown in the figure.
The acceleration of gravity is 9.81 m/s2 .

A) What is the minimum coefficient of static
friction such that the objects remain at rest?

I already got part A which is 0.833, but need help on B


B) If the coefficient of static friction is less than
that found above, and if the coefficient of
kinetic friction between the block and the
table is 0.2, find the time it takes for the 5 kg
mass to fall 9 m to the floor if the system
starts from rest.
Answer in units of s

In order to calculate the time taken to fall to the floor, you need the acceleration.

In order to find the acceleration of the 11 kg combination, you need the net force.

The net force will be the sum of the friction on the 6kg mass, and the weight of the 5 kg mass. Add those two as vectors, as one is promoting motion while the other is trying to stop it.