Min force to lever to lift weight

[toforfiltum]

Homework Statement

Homework Equations

Concept of couple?

The Attempt at a Solution

First, I calculated the couple about disc, though I'm not sure if I can use this approach. Since 900 N is pulling the string of pulley downwards, I take the couple about disc as 900 x 0.4, which gives me 360 Nm. To balance this couple, the couple by F must be equal to 360. So 1.2 x F = 360 which gives me 300 N as the answer. But I'm wrong, since the answer is B. Where did I go wrong?

 

[Bystander]

Where did I go wrong?

900 x 0.4,

Any particular reason for using diameter?

 

[toforfiltum]

Any particular reason for using diameter?

I thought the 900 N exerts a couple on the disc, though I'm not sure. I'm just guessing.

 

[Bystander]

What are/would be the two elements of the couple?

 

[toforfiltum]

What are/would be the two elements of the couple?

Two forces acting in opposite directions separated by a perpendicular distance.

 

[Bystander]

What specific forces? And what distance?

 

[toforfiltum]

What specific forces? And what distance?

In this case there's only one force which is 900 N rotating the disc in anticlockwise direction.

 

[Bystander]

What's holding the disc?

 

[toforfiltum]

What's holding the disc?

The lever turning in opposite direction?

 

[Bystander]

What's the "spindle" doing?

 

[toforfiltum]

What's the "spindle" doing?[/

Transferring the energy?

 

[Bystander]

No sideways forces on it?

 

[toforfiltum]

No sideways forces on it?

I totally don't know. From the picture, as the spindle rotates, it turns discs in opposite direction to the wight of 900 N on disc.

 

[Bystander]

What happens when you pull the starter rope on a lawnmower without putting your foot on the mower to hold it in place?

 

[toforfiltum]

What happens when you pull the starter rope on a lawnmower without putting your foot on the mower to hold it in place?

The lawnmower will jump?

 

[Bystander]

jump?

Any particular direction?

 

[toforfiltum]

Any particular direction?

I've never used a lawnmower before so I'm not too sure.It will jump away from the person pulling it?