Conservation of Energy and frictionless pulley?

In summary, a 20.0 kg block is connected to a 30.0 kg block by a string over a frictionless pulley. The 30.0 kg block is connected to a spring with a force constant of 240 N/m. The system is initially at rest with the spring unstretched and the incline is frictionless. The 20.0 kg block is pulled 18.0 cm down the incline and released. The question is to find the speed of each block when the 30.0 kg block is 20.0 cm above the floor. The relevant equation is (K+U)initial=(K+U)final. The answer given is 1.1687 m/s^
  • #1
Eukanuba863
4
0

Homework Statement


A 20.0 kg block is connected to a 30.0 kg block by a string that passes over a light, frictionless pulley. The 30.0 kg block is connected to a spring that has negligible mass and a force constant of 240 N/m, as shown in the figure below. The spring is unstretched when the system is as shown in the figure, and the incline is frictionless. The 20.0 kg block is pulled 18.0 cm down the incline (so that the 30.0 kg block is 38.0 cm above the floor) and released from rest. Find the speed of each block when the 30.0 kg block is 20.0 cm above the floor (that is, when the spring is unstretched).



Homework Equations



(K-U)sub(i)=(K-U)sub(f)

The Attempt at a Solution



i've talked with multiple physics teachers on this problem every body got different anwsers...

i'm almost convinced the anwser is 1.1687 m/s^2

Could you help me please?
 
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  • #2
I need to see the figure. I can't tell the angle of the incline, wether there is one or 2 springs, and in what direction they pull etc.
 
  • #3
here is the image...

A 20.0 kg block is connected to a 30.0 kg block by a string that passes over a light, frictionless pulley. The 30.0 kg block is connected to a spring that has negligible mass and a force constant of 240 N/m, as shown in the figure below. The spring is unstretched when the system is as shown in the figure, and the incline is frictionless. The 20.0 kg block is pulled 18.0 cm down the incline (so that the 30.0 kg block is 38.0 cm above the floor) and released from rest. Find the speed of each block when the 30.0 kg block is 20.0 cm above the floor (that is, when the spring is unstretched).

p7-45.gif
 
  • #4
Eukanuba863 said:

Homework Equations



(K-U)sub(i)=(K-U)sub(f)
You want conservation of energy--that's not quite it. Mechanical energy equals KE + PE. (You have multiple forms of PE to track in this problem.)
i'm almost convinced the anwser is 1.1687 m/s^2
Show how you got that.
 
  • #5
i know the parts just will you check my aritmatic?

it's

(K+U)initial=(K+U)final

and i know all the spring constant parts with .5kx^2, mgh etc.
 
  • #6
please

could you just check my arithmetic please?
 
  • #7
Show us your arithmetic so we can check it.
 

FAQ: Conservation of Energy and frictionless pulley?

1. What is the law of conservation of energy?

The law of conservation of energy states that energy cannot be created or destroyed, but can only be transformed from one form to another.

2. How does the law of conservation of energy apply to a frictionless pulley system?

In a frictionless pulley system, the law of conservation of energy still applies. The total amount of energy in the system remains constant, even though the energy may be transferred between different forms such as potential and kinetic energy.

3. What is a frictionless pulley and how does it work?

A frictionless pulley is a type of pulley that has no friction between its moving parts. It works by using two ropes or cables to support a load and distribute its weight evenly. This allows for the load to be lifted with less effort and energy.

4. What are some real-world applications of the conservation of energy and frictionless pulleys?

The conservation of energy and frictionless pulleys have many real-world applications, such as in elevators, cranes, and other lifting mechanisms. They are also used in engineering and physics experiments to demonstrate the principles of energy conservation.

5. What are the limitations of the conservation of energy and frictionless pulleys in practical applications?

In practical applications, there may be external factors such as air resistance or friction that can affect the amount of energy in a system. Additionally, in a real-world frictionless pulley system, there may be some amount of friction present, which can cause a loss of energy. These factors must be taken into account when applying the principles of conservation of energy and frictionless pulleys in practical situations.

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