An object with a mass of #18 kg# is hanging from an axle with a radius of #16 cm#. If the wheel attached to the axle has a radius of #28 cm#, how much force must be applied to the wheel to keep the object from falling?

1 Answer
Jul 1, 2018


Force on wheel = 100.8N (in opposite direction)


force due to gravity s 9.8N/kg (=176.4N for 18kg object)

turning moment is force*radius
remember to convert to standard units (metres, Newtons, etc.)

object's turning moment (a.k.a. torque) will be :

#M(object) = 18*9.8*0.16 = 28.224# Nm

to prevent the axle turning the sum of the moments must be zero

#F(wheel)*r(wheel) + F(object)*r(object) = 0#

#F(wheel)*0.28 + 28.224 = 0#

#F(wheel) = -28.224/0.28 = -100.8 N#

the negative value means the force is applied in the opposite direction to that due to the object