Net work and kinetic energy (pushing a wagon to accelerate it)

In summary, the conversation discusses the confusion of using different values for work in the kinetic energy equation and questions why friction is not taken into account. The expert confirms that the net work equals the change in kinetic energy and asks for clarification on the answer and the mass of the wagon.
  • #1
aqryus
6
1
Homework Statement
Bill does 500J of work on a wagon, friction does work of -200J. What is the final speed of the wagon if it starts at rest?
Relevant Equations
w=fdcostheta
Ek=1/2mv^2
I'm a little confused because my teacher used Bill's 500J of work for the kinetic energy equation and I don't understand why. I used the net work, so 300J, to find the speed and I'm not sure why that's wrong. Wouldn't friction make the wagon move slower than if there was no friction? So why isn't that accounted for in the kinetic energy equation to find speed? Thank you
 
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  • #2
You are correct. The net work done on the wagon equals the change in the kinetic energy of the wagon. What did you get for the answer? Was the mass of the wagon specified?
 

FAQ: Net work and kinetic energy (pushing a wagon to accelerate it)

What is net work in the context of pushing a wagon?

Net work refers to the total work done by all the forces acting on the wagon. It is the sum of the work done by each individual force, including applied forces, frictional forces, and any other forces that might be acting on the wagon.

How is net work related to kinetic energy?

Net work is directly related to the change in kinetic energy of the wagon. According to the work-energy theorem, the net work done on an object is equal to the change in its kinetic energy. Mathematically, this is expressed as \( W_{\text{net}} = \Delta KE \), where \( W_{\text{net}} \) is the net work and \( \Delta KE \) is the change in kinetic energy.

How do you calculate the net work done on a wagon?

To calculate the net work done on a wagon, you need to determine the work done by each force acting on it. Work is calculated as the product of the force and the displacement in the direction of the force: \( W = F \cdot d \cdot \cos(\theta) \), where \( F \) is the force, \( d \) is the displacement, and \( \theta \) is the angle between the force and the direction of displacement. Sum up the work done by all forces to get the net work.

What factors affect the kinetic energy of the wagon?

The kinetic energy of the wagon depends on its mass and its velocity. The kinetic energy (KE) is given by the equation \( KE = \frac{1}{2}mv^2 \), where \( m \) is the mass of the wagon and \( v \) is its velocity. Therefore, any change in the mass or velocity of the wagon will affect its kinetic energy.

How does friction impact the net work and kinetic energy when pushing a wagon?

Friction opposes the motion of the wagon and does negative work, which reduces the net work done on the wagon. As a result, the kinetic energy gained by the wagon is less than it would be if there were no friction. The work done by friction is subtracted from the work done by the applied force to determine the net work.

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