A uniform rod has a weight of 40 N and a length of 1 m. It is hinged to a wall (

Question

A uniform rod has a weight of 40 N and a length of 1 m. It is hinged to a wall (at the left end), and held in a horizontal position by a vertical massless string (at the right end). What is the magnitude of the torque exerted by the string about a horizontal axis which passes through the hinge and is perpendicular to the rod? 5 N-m 10 N-m 20 N-m 40 N-m 2. A uniform rod has a length of 2 m. It is hinged to a wall (at the left end), and held in a horizontal position by a vertical massless string (at the right end) . What is the angular acceleration of the rod at the moment the string is released?

Explanation / Answer

Number 1)

The string must balance the torque created by the weight

Torque = Fr = (40)(.5)

Torque = 20 Nm (Choice C)

Number 2)

Torque = I(alpha)

Fr = I(alpha)

I = (1/12 ml2) for the rod

mgr = (1/12)(ml2)(alpha) mass cancels

(9.8)(1) = (1/12)(2)2(alpha)

alpha = 29.4 rad/s2

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