I am stuck on a simple question that I belive could be a trick.
it says -
A 50kg body hangs at rest from a rope wrapped around a pully 15cm in diameter. what is the torque about the axis?
the formula I have used for a similar question is
Torque = Force x distance
Force= Mass x Acceleration
seeing as there is no acceleartion in this problem do i assume that Force is equal to 50kg ie 50Newtons or should i have to mulitiply by gravity (9.81) and assume this is the accelartion?
would the distance be 15cm or .15m and where is the axis of a pulley?? :confused: please help
May 1st 2005, 03:59 PM
Free Body Diagram
The torque about the axis should be the force, T, of the Tension in the rope multiplied by the radius, r, of the pulley.
If you do a free body diagram of the 50kg body you have the force, T, pulling up on the body and the weight of the body which is either 50kg*9.81m/s^2 or 50N they are equivalent.
T = mg
T = 50N
The radius, r, of the pulley is either .15m or 15cm they are also equivalent.
So the torque, J, is equal to 50N * .15m or, J = 7.5 Nm