Solving a Homework Problem with Mass, String, and Friction

In summary: If the 'm' on the left side of the equality is neglected, then the problem seems to be impossible to solve.In summary, the conversation discusses two blocks of different masses connected by an ideal string, with one block descending at a constant speed due to the absence of friction. The question is which of the given options is true, with the correct answer being the first option. The reasoning behind this is that since the speed is constant, there is no acceleration, and thus the sum of the forces acting on the system is zero. By decomposing gravity into its components, the solution can be found using trigonometry.
  • #1
SqueeSpleen
141
5

Homework Statement


There's two blocks of mass m_{A} and m_{B} which are linked by an ideal string. The block of mass A descends at constant speed. There's no friction. If the pulley is ideal, which one of the following is true[/B]
upload_2017-5-19_0-33-15.png

Homework Equations


Newton laws and trigonometry I think.[/B]

The Attempt at a Solution


I think that the correct answer is the second one, but the first one is marked as correct so I wanted a second opinion.
My reasoning is the following: If the speed is constant it means there is no acceleration, so the sum of the forces is 0. Then I decomposed gravity in the component that's compensated by the normal force done by the triangle and it's perpendicular component. So I arrived to
m_{A} (1/2) = m_{B} sqrt(3)/2
Now that I check, it isn't item 2. it would fall in item 1 as 1/sqrt(3) is between 0.25 and 0.6
Right?

sorry for the typos, I broke my keyboard yesterday (I won't drink coffee while on computer again) and I'm with a rubber one until a new one arrives, at least it's better thanthe one that windows have to use with the mouse.

[/B]
 

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  • #2
Working it out very quickly, and thus prone to error, I think the first answer is correct.
 
  • #3
SqueeSpleen said:
it would fall in item 1 as 1/sqrt(3) is between 0.25 and 0.6
Right?
Yes.
 
  • #4
Absolutely correct! Way of solving by simply taking their Sine components of 'g' and solve it.
 

1. How do I calculate the force of friction in a homework problem with mass, string, and friction?

The force of friction can be calculated using the formula F = μN, where μ is the coefficient of friction and N is the normal force. In this case, the normal force would be equal to the weight of the object, and the coefficient of friction can be found in a table or given in the problem.

2. What is the role of the string in a homework problem involving mass, string, and friction?

The string in these types of problems is typically used to apply a force to the object. This force can be either horizontal or vertical, and it can be used to calculate the acceleration or tension in the string.

3. How do I incorporate the mass of the object into the problem?

The mass of the object is an important factor in these types of problems because it affects the weight, normal force, and acceleration of the object. Make sure to include the mass in any relevant equations and calculations.

4. What are the units of measurement for the variables in this type of problem?

The units of measurement will depend on the specific variables in the problem. For example, the mass will be measured in kilograms, the force in Newtons, and the coefficient of friction is unitless. Make sure to pay attention to the units and convert them if necessary.

5. How can I check if my solution to the problem is correct?

You can check your solution by using the laws of physics and basic principles to see if your answer makes sense. You can also double check your calculations and make sure you are using the correct equations and variables. It can also be helpful to compare your answer to the given answer or ask a teacher or classmate for verification.

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