A Question About Pulleys and Spring Scales

In summary, the students are trying to find what the spring scale reads on a massless string hanging from a frictionless pulley. The answer was incorrectly stated to be in kg, when it should be in Newtons. However, the problem is that they want the answer in kg, not Newtons. If they could post a picture of the setup, it would help to clarify the question.
  • #1
mcnealymt
35
0

Homework Statement


The question shows two 5kg masses at rest hanging from two pulleys on opposite ends of a table. The string is massless and the pulley is frictionless.


Homework Equations


They want to know what the spring scale reads (in the middle of the masslessstring).

The Attempt at a Solution


This is what I thought:

Fspring= w=mg
5kg*9.8m/s^2= 49N
This answer was wrong.

Would the answer be 98N since both masses are the same?
 
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  • #2
mcnealymt said:
They want to know what the spring scale reads (in the middle of the masslessstring).
Assuming I understand the setup, the spring scale will read the tension in the string.

Fspring= w=mg
5kg*9.8m/s^2= 49N
This answer was wrong.
I'd say that answer was correct. Why do you think it's wrong?

Would the answer be 98N since both masses are the same?
No.
 
  • #5
I must be going crazy . What about the mass of the system? Wouldn't it be 10?
 
Last edited:
  • #6
mcnealymt said:
What about the mass of the system? Wouldn't it be 10?
If by "system" you mean both 5 kg masses together, then sure.

What are the exact questions you are being asked?
 
  • #7
The string is massless and the pulley is frictionless. The spring sclae reads in kg. What is the reading of the scale?
 
  • #8
mcnealymt said:
The spring sclae reads in kg.
There's the problem: They want the answer in kg, not Newtons.
 
  • #9
So wouldn't the answer just be five because 49N is 5kg.
 
  • #10
mcnealymt said:
So wouldn't the answer just be five because 49N is 5kg.
Yes, the answer will be 5 kg.
 
  • #11
Thank you Doc Al. I highly appreciate it.
 

What is a pulley and how does it work?

A pulley is a simple machine that consists of a wheel with a grooved rim and a rope or cable wrapped around it. It is used to change the direction of a force, typically to lift or move objects. When a force is applied to the rope, the pulley rotates and the object attached to the rope moves in the desired direction.

What are the different types of pulleys?

There are three main types of pulleys: fixed, movable, and compound. Fixed pulleys have a stationary axle and are used to change the direction of a force. Movable pulleys have a movable axle and are used to increase the mechanical advantage of a system. Compound pulleys combine fixed and movable pulleys to create an even greater mechanical advantage.

What is a spring scale and how does it work?

A spring scale is a device used to measure weight or force. It consists of a coiled spring that stretches when a force is applied to it. As the spring stretches, it exerts a force equal to the weight or force applied to it. This force can be read on a scale attached to the spring.

How do pulleys and spring scales work together?

Pulleys and spring scales can work together in a system to measure weight or force. The object being weighed is attached to the pulley, which is connected to the spring scale. As the object is lifted, the spring scale measures the force exerted on the pulley by the weight of the object. This force can then be converted to weight using the appropriate conversion factor.

What are some real-life applications of pulleys and spring scales?

Pulleys and spring scales have many practical uses in our daily lives. Some examples include weighing produce at the grocery store, lifting heavy objects with a crane, and measuring the weight of a person on a scale. They are also commonly used in scientific experiments and in industrial settings for measuring force and weight.

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