Magnitude of a block?

Question

A 140 N block rests on a table. The suspended
mass has a weight of 69 N.

What is the magnitude of the minimum
force of static friction required to hold both
blocks at rest? Answer in units of N.

What minimum coeffcient of static friction
is required to ensure that both blocks remain
at rest?

Answer 1

1. 69 N

2. μ(s) = 0.493

Since both blocks are at rest, they're in equilibrium. For the larger block, that means that the force exerted on it by the other block is counteracted by frictional force, i.e., they're equal. The applied force is the weight of the second block, 69 N.

For the coefficient of static friction,

μW = F, or 140 μ = 69

Thence, μ = 0.493

Answer 2

69/140

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