Two forces try to rotate a solid disc around its central axis \"A\". The forces

Question

Two forces try to rotate a solid disc around its central axis "A". The forces act at different points away from the centre of the disc as show on the diagram. The magnitude of the forces are |F1| = 5 N and |F2| = 6 N, and the distances are n = 2 m and r2 = 1 m. The angle between F1 and the horizontal is theta = 30 degree, and the angle between F2 and the vertical is phi = 60 degree. Find the line of action (also called the moment of arm) for each of these forces. Determine the magnitude and direction of torque that each force exert on the disk. Find the net torque exerted on the disk. Which way does this torque point?

Explanation / Answer

give,

F1 = 5 N making 30 degree with horizontal

F2 = 6 N making angle of 60 degree with vertical

line of action is the direction in with forca is acting, dashed lines in the diagram showing the line of action

torque = force * perpendicular distance

torque due to F1 = 5 * 2 * sin(30)

torque due to F1 = 5 Nm

Torque due to F2 = 6 * 1 * cos(60)

Torque due to F2 = 3 Nm

both the torque are in opposite direction so,

net torque = 5 - 3

net torque = 2 Nm, direction of the torque is -z axis or inside the page

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