Calculating Pulley Forces: A Frustrating Problem

In summary, the conversation involves a person struggling with a pulley question. They have calculated T1 and T2, but the answer provided is different from their calculation. The expert advises to draw a free body diagram and take into consideration the force from the person pulling on the rope. The person also mentions a box in the situation and asks for clarification on its position.
  • #1
kuany
1
0
this is a simple pulley question but i can't seem to get it right
the person which i hav very badly drawn weighs 80kg and I'm trying to calculate P.
This is wat I hav done, please tell me wat I hav done wrong.
1st i calculated T1:
80*9.81=784.8
T1= 784.8/2
=392.4
and to calculate T2:
T2= 392.4/2
= 196.2
and T2=P
but the answer says that P=157

Please help me I'm becoming very frustrated.
Thank you.
 

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  • #2
For a start, your first step is wrong.

The chap is pulling on the rope too, - T1 isn't just half the force from the bosun's weight.

You've got the right idea though; tensions either side of the pulley being equal. Draw free body diagrams for each pulley, the bosun, and the support, and take it from there.
 
  • #3
The box he is sitting on has only one cable at the left end so the box would rotate under his weight, unless there is some other information you are not giving. Is the box supposed to be in the air or sitting on the ground?
 

1. What is a pulley and how does it work?

A pulley is a simple machine consisting of a wheel with a groove around its circumference, through which a rope or belt is passed. It can also refer to a system of multiple pulleys working together. The pulley works by changing the direction of the force applied to the rope or belt, allowing for the lifting or pulling of heavy objects with less effort.

2. Why is calculating pulley forces considered a frustrating problem?

Calculating pulley forces can be frustrating because it involves multiple factors and variables, such as the weight of the object being lifted, the number of pulleys used, and the angle of the rope or belt. It requires knowledge of physics and mathematical equations, and even a small error in calculation can greatly affect the accuracy of the result.

3. What is the formula for calculating pulley forces?

The formula for calculating pulley forces is F = (m1 + m2 + ...) x g, where F is the total force, m1 and m2 are the masses of the objects being lifted, and g is the acceleration due to gravity (9.8 m/s^2). This formula assumes an ideal pulley system with no friction.

4. How do you take friction into account when calculating pulley forces?

To take friction into account, you can use the equation F = (m1 + m2 + ...) x g + μ x Fn, where μ is the coefficient of friction and Fn is the normal force. The coefficient of friction can vary depending on the materials of the pulley and the rope or belt, and the normal force is equal to the weight of the object being lifted.

5. What are some tips for accurately calculating pulley forces?

Some tips for accurately calculating pulley forces include ensuring that all units are consistent (e.g. using kilograms for mass and meters for distance), accounting for friction and any other external forces, and double-checking all calculations. It may also be helpful to draw a diagram of the pulley system to better visualize the forces at play.

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