When is work positive or negative when sawing a tree with a handsaw?

  • Thread starter Raikou Tatsu
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In summary, work is a scalar quantity that can be positive or negative depending on the direction of the applied force and displacement. In the case of sawing a tree, the work done by the person pushing and pulling the saw is positive because the force and displacement are in the same direction. The work done by the tree's force on the saw is negative. Remember that work is positive when the force and displacement are in the same direction, and negative when they are in opposite directions.
  • #1
Raikou Tatsu
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lets say you have a handsaw and you a sawing a tree by pushing the saw away from you and pulling it toward you. you are doing work when you push and when you pull the saw but when is the work positive or negative. or is the work positive during both the pushing and pulling
 
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  • #2
Its positive both ways, since you are losing energy both times.
 
  • #3
The easy way to know if you ae doing poitive or negative work is to look for solving the expression W=F.s , in the above case , since you apply force forwards and the saw displaces forward , so the dot product will be poitive sice cos0=1 , and same is the case when you pull the saw towards yourself.

BJ
 
  • #4
Work is a scalar quantity. Here is + and - sign gives whether the work is done by that force or done against the force i.e. whether the energy is supplied by the system applying force of the energy is supplied to the system

In your example the work done by you is positive in both cases but work done by the force applied by the tree on the saw is negative.
 
  • #5
Work done by a force

Raikou Tatsu, The force in we are talking about is the one that you are exerting on the saw when you are pushing it away from you , Ff, and pulling it towards you, Fb. In both cases the displacement of the saw is in the same direction as the applied force. Therefore the work done is positive in both case - see the attached drawing.
 

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  • #6
To remember if it's + or -,
+ when the force and the displacement are in the same direction.
- when the force and the displace are in opposite direction.
Sor your answer must +
 

1. What is positive work?

Positive work in science refers to the action of a force that results in the displacement of an object in the same direction as the applied force. In other words, when a force is applied to an object and the object moves in the same direction as the force, positive work is done on the object.

2. How is positive work calculated?

The formula for calculating positive work is W = F * d * cosθ, where W represents work, F is the applied force, d is the displacement of the object, and θ is the angle between the direction of the force and the direction of the displacement.

3. What is negative work?

Negative work in science refers to the action of a force that results in the displacement of an object in the opposite direction of the applied force. This means that the force and the displacement are in opposite directions, causing negative work to be done on the object.

4. How is negative work represented on a graph?

Negative work is represented as a line with a negative slope on a graph, since the force and displacement are in opposite directions. The area under the line represents the amount of negative work done on the object.

5. What is the difference between positive and negative work?

The main difference between positive and negative work is the direction of the force and displacement. Positive work is done when the force and displacement are in the same direction, while negative work is done when they are in opposite directions. Another difference is that positive work results in an increase in the kinetic energy of the object, while negative work results in a decrease in kinetic energy.

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