Question

Four forces are applied to a box sitting on a horizontal floor. The normal is 112 N. The friction is 41.2 N. The standard position angle of the pull is 27 degrees. Warning: the weight and the normal are not equal.

A) Calculate the magnitude of the pull.

B) Calculate the magnitude of the weight.

Answer 1

From above FBD:

Using Force balance on the box in horizontal direction:

Fx_net = T*cos - Ff

Fx_net = 0, since only four forces are applied, So net force is zero (N, Ff, T, W)

T*cos = Ff

T = Ff/cos

Using given values:

T = 41.2/cos 27 deg

T = Magnitude of the pull force = 46.24 N

Part B.

Using force balance in vertical direction:

Fy_net = N + T*sin - W

W = Weight force = N + T*sin

W = 112 + 46.24*sin 27 deg

W = Magnitude of Weight = 133.0 N

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