Wheelbarrow and load advantage (i think)

[armbrecht]

Homework Statement

A wheelbarrow is holding a mass of 15kg, 35cm from the handle. The fulcrum is located 65cm from the handle. What is the mechanical advantage at the handle?

Handle Load Fulcrum
_______________============_
____________ O (wheel)

Homework Equations

I believe it is (f1)x(d1)=(f2)x(d2)

The Attempt at a Solution

Therefore ...
(f1)x(65)=(15)x(30) 30 being the distance from the handle to the centre of load.
(f1)x(65)=450
f1=450 / 65
f1=6.9 kg

Is this correct? I am a complete dummy at physics :(

 

[redargon]

no, unfortunately you made a slight calculation error, but the rest is ok. your distance from the handle to the centre of the load is 35, not 30. Also, the term "mechanical advantage" gives me the feeling your answer should be in a ration or percentage form. ie. If I lifted the 15kg mass directly, it's mass is 15kg, if I use the wheelbarrow, it's apparent mass is 6.9kg. Therefore I have a mechanical advantage of 15/6.9=2.17 or (15-6.9)/6.9=117%

Also, the wheel of your wheelbarrow is the fulcrum and it appears to be in a strange positon on your drawing. To approach this problem more accurately, you should draw a free body diagram, state that the system is equilibrium and let the sum of moments about your fulcrum be zero. You'll end up with the same result, but it will be neater and more rigid.

 

[nlightner]

Yes, your calculation for the force at the handle (f1) is correct. This means that for every 1 kilogram of force applied at the handle, there is a 6.9 kilogram force acting on the load. This is known as the mechanical advantage, which in this case is 6.9. This means that the wheelbarrow is able to lift a load that is 6.9 times heavier than the force applied at the handle. This is due to the use of a lever and the distance between the handle and the fulcrum, which allows for a smaller force to lift a larger load.