Forces problem involving rotational motion.

[NJDevilsFan26]

A cord is wrapped around the rim of a solid uniform wheel 0.240m in radius and of mass 8.80kg. A steady horizontal pull of 30.0N to the right is exerted on the cord, pulling it off tangentially from the wheel. The wheel is mounted on frictionless bearings on a horizontal axle through its center.

Find the magnitude of the force that the axle exerts on the wheel.

-I tried to say that the normal force is equal to mg, which is the incorrect answer. I do not understand why the force is =/=mg.

Any helpful comments are appreciated.

 

[jbsteele]

The force that the axle exerts on the wheel is equal to the sum of the tangential force (30.0 N) and the normal force, which is the reaction force from the ground caused by the wheel's weight (8.80 kg x 9.81 m/s2 = 86.6 N). Therefore, the total force that the axle exerts on the wheel is 116.6 N.