A 6 kg block rests on a horizontal table, attached to a 3 kg block by a light st

Question

A 6 kg block rests on a horizontal table, attached to a 3 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? 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 0.3, find the time it takes for the 3 kg mass to fall 3 m to the floor if the system starts from rest. Answer in units of s

Explanation / Answer

1) for objects to remain at rest,

3g- T=0

T=3g

T-6g=0

min = 3g/6g

= 0.5

2) again

3g - T = 3a

T- (0.3*6g)= 6a

adding,

1.2 g= 9a

a=1.31 m/s2

Using 2nd eqn of motion,

3= (1/2)*1.31*t2

t= 2.14 s

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