Lawn Mower

1. May 23, 2007

Lilkaze

Here is the question that I don't understand :

When cutting grass with a lawn mower, a worker can either push or pull it. Using physics concepts, compare the difficulty of the job when the worker pushes the lawn mower or pulls the lawn mower

Pushing or pulling will be easier to do the work ? And, what are the reasons ?

2. May 23, 2007

husky88

You can think of what forces are acting.
There is the force of gravity, the normal force and the force of friction.
Then there is the force you pull or push with.
When you pull, you pull slightly upwards, reducing the normal force on the lawn mower.
When you push, you push slightly downwards, increasing the normal force on the lawn mower.
Why you do more work is because of force of friction. So...

3. May 23, 2007

Lilkaze

When moving the lawn mower, it is of course easier to pull it. But in cutting the grass, is it easier to push it ? Assuming that the total force acting on the grass is higher and therefore, the job will be easier ?

4. May 23, 2007

husky88

Well you could put it that way.
But we are assuming that your blades are sharp enough and that you actually don't exert any force to cut it. The engine exerts the force to cut it.
You only exert the force to move it.