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1.) The figure below shows a pulley winding a load of 100kg upwards, from rest. The load accelerates at 0.4ms-2, and the friction force between the rope and the pulley is equivalent to 20N.

Determine;
a.) The applied torque
b.) The work done during one revolution of the pulley
c.) The power dissipated







2.) A centrifugal clutch has four shoes, each of which has a mass of 1.25kg. The shoes are held in to the centre of the clutch by springs with a stiffness of 8KNm-1. The internal diameter of the friction surface is 500mm and the radius of the centre of gravity of the shoes is 200mm. There is a gap of 18mm between the shoes and the inside of the drum when the clutch is static. The coefficient of friction is 0.22, Determine;
a.) The rotational speed at which the clutch engages

b.) The power transmitted at 1300rpm

Tom:

The figures did not come through?

Are these questions as part of an academic assignment? If so asking for more than general guidance violates the academic integrity of your school.

Niel Leon
engineering.com

Hi neil,
This is not part of an exam or assignement. They are work examples from a training pack, which will help us get through our end of year exam. But i am struggling with the two above examples. For some reason the image is not coming up, but if any one has an idea what to do, i can email it as i have typed it up from my example sheet. thanks

You need to go back to basics:

1a. What is torque?

It is force times the lever arm length

1b. What is work

This is force time distance traveled. For one revolution of pulley that distance = pi * diameter

1c. Power is Energy / unit time. Total power = total work = Weight*distance + Friction*distance

This should give you a start. Hints for question 2 later.


Niel

I have managed to do 1a & 1b and all of 2. but i am just stuck on 1c. Is it torque*angular velocity? My exam is on wednesday. so i am studying just about all aspects atm and stuck on this one. cheers

Tom: Have you read up on the basics of power dissipation? Here's a nifty tool: http://www.engineeringtoolbox.com/l...d_872.html

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